Re: [RFC,v2] Bluetooth: hci_qca: Collect controller memory dump during SSR
From: Marcel Holtmann
Date: Fri Jan 18 2019 - 03:54:38 EST
Hi Balakrishna,
>>>>> We will collect the ramdump of BT controller when hardware error event
>>>>> received before rebooting the HCI layer. Before restarting a subsystem
>>>>> or a process running on a subsystem, it is often required to request
>>>>> either a subsystem or a process to perform proper cache dump and
>>>>> software failure reason into a memory buffer which application
>>>>> processor can retrieve afterwards. SW developers can often provide
>>>>> initial investigation by looking into that debugging information.
>>>>> Signed-off-by: Balakrishna Godavarthi <bgodavar@xxxxxxxxxxxxxx>
>>>>> ---
>>>>> changes v2:
>>>>> * entirely an newer approach handling with an work queue.
>>>>> ---
>>>>> drivers/bluetooth/hci_qca.c | 289 ++++++++++++++++++++++++++++++++++--
>>>>> 1 file changed, 278 insertions(+), 11 deletions(-)
>>>>> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
>>>>> index f036c8f98ea3..62b768bc32ec 100644
>>>>> --- a/drivers/bluetooth/hci_qca.c
>>>>> +++ b/drivers/bluetooth/hci_qca.c
>>>>> @@ -32,6 +32,7 @@
>>>>> #include <linux/clk.h>
>>>>> #include <linux/debugfs.h>
>>>>> #include <linux/delay.h>
>>>>> +#include <linux/devcoredump.h>
>>>>> #include <linux/device.h>
>>>>> #include <linux/gpio/consumer.h>
>>>>> #include <linux/mod_devicetable.h>
>>>> don't we have some crashdump core facility that could be utilized here?
>>> [Bala]: no i don't think so. that is reason calling devcoredump.h
>> what is wrong with using devcoredump.h?
>
> [Bala]: using the devcoredump.h
>
>>>>> @@ -57,9 +58,10 @@
>>>>> /* Controller states */
>>>>> #define STATE_IN_BAND_SLEEP_ENABLED 1
>>>>> -#define IBS_WAKE_RETRANS_TIMEOUT_MS 100
>>>>> +#define IBS_WAKE_RETRANS_TIMEOUT_MS 100
>>>>> #define IBS_TX_IDLE_TIMEOUT_MS 2000
>>>>> -#define BAUDRATE_SETTLE_TIMEOUT_MS 300
>>>>> +#define BAUDRATE_SETTLE_TIMEOUT_MS 300
>>>>> +#define MEMDUMP_COLLECTION_TIMEOUT_MS 8000
>>>>> /* susclk rate */
>>>>> #define SUSCLK_RATE_32KHZ 32768
>>>>> @@ -67,6 +69,13 @@
>>>>> /* Controller debug log header */
>>>>> #define QCA_DEBUG_HANDLE 0x2EDC
>>>>> +/* Controller dump header */
>>>>> +#define QCA_SSR_DUMP_HANDLE 0x0108
>>>>> +#define QCA_DUMP_PACKET_SIZE 255
>>>>> +#define QCA_LAST_SEQUENCE_NUM 0xFFFF
>>>>> +#define QCA_CRASHBYTE_PACKET_LEN 1100
>>>>> +#define QCA_MEMDUMP_BYTE 0xFB
>>>>> +
>>>>> /* HCI_IBS transmit side sleep protocol states */
>>>>> enum tx_ibs_states {
>>>>> HCI_IBS_TX_ASLEEP,
>>>>> @@ -89,12 +98,41 @@ enum hci_ibs_clock_state_vote {
>>>>> HCI_IBS_RX_VOTE_CLOCK_OFF,
>>>>> };
>>>>> +/* Controller memory dump states */
>>>>> +enum qca_memdump_states {
>>>>> + QCA_MEMDUMP_IDLE,
>>>>> + QCA_MEMDUMP_COLLECTING,
>>>>> + QCA_MEMDUMP_COLLECTED,
>>>>> + QCA_MEMDUMP_TIMEOUT,
>>>>> +};
>>>>> +
>>>>> +struct qca_memdump_data {
>>>>> + char *memdump_buf_head;
>>>>> + char *memdump_buf_tail;
>>>>> + u32 current_seq_no;
>>>>> + u32 received_dump;
>>>>> +};
>>>>> +
>>>>> +struct qca_memdump_event_hdr {
>>>>> + __u8 evt;
>>>>> + __u8 plen;
>>>>> + __u16 opcode;
>>>>> + __u16 seq_no;
>>>>> + __u8 reserved;
>>>>> +} __packed;
>>>>> +
>>>>> +
>>>>> +struct qca_dump_size {
>>>>> + u32 dump_size;
>>>>> +} __packed;
>>>>> +
>>>>> struct qca_data {
>>>>> struct hci_uart *hu;
>>>>> struct sk_buff *rx_skb;
>>>>> struct sk_buff_head txq;
>>>>> - struct sk_buff_head tx_wait_q; /* HCI_IBS wait queue */
>>>>> - spinlock_t hci_ibs_lock; /* HCI_IBS state lock */
>>>>> + struct sk_buff_head tx_wait_q; /* HCI_IBS wait queue */
>>>>> + struct sk_buff_head rx_memdump_q; /* Memdump wait queue */
>>>>> + spinlock_t hci_ibs_lock; /* HCI_IBS state lock */
>>>>> u8 tx_ibs_state; /* HCI_IBS transmit side power state*/
>>>>> u8 rx_ibs_state; /* HCI_IBS receive side power state */
>>>>> bool tx_vote; /* Clock must be on for TX */
>>>>> @@ -103,12 +141,17 @@ struct qca_data {
>>>>> u32 tx_idle_delay;
>>>>> struct timer_list wake_retrans_timer;
>>>>> u32 wake_retrans;
>>>>> + struct timer_list memdump_timer;
>>>>> + u32 memdump_delay;
>>>>> struct workqueue_struct *workqueue;
>>>>> struct work_struct ws_awake_rx;
>>>>> struct work_struct ws_awake_device;
>>>>> struct work_struct ws_rx_vote_off;
>>>>> struct work_struct ws_tx_vote_off;
>>>>> + struct work_struct ctrl_memdump_evt;
>>>>> + struct qca_memdump_data *qca_memdump;
>>>>> unsigned long flags;
>>>>> + enum qca_memdump_states memdump_state;
>>>>> /* For debugging purpose */
>>>>> u64 ibs_sent_wacks;
>>>>> @@ -173,6 +216,7 @@ struct qca_serdev {
>>>>> static int qca_power_setup(struct hci_uart *hu, bool on);
>>>>> static void qca_power_shutdown(struct hci_uart *hu);
>>>>> static int qca_power_off(struct hci_dev *hdev);
>>>>> +static void qca_controller_memdump(struct work_struct *work);
>>>>> static void __serial_clock_on(struct tty_struct *tty)
>>>>> {
>>>>> @@ -446,6 +490,21 @@ static void hci_ibs_wake_retrans_timeout(struct timer_list *t)
>>>>> hci_uart_tx_wakeup(hu);
>>>>> }
>>>>> +static void hci_memdump_timeout(struct timer_list *t)
>>>>> +{
>>>>> + struct qca_data *qca = from_timer(qca, t, tx_idle_timer);
>>>>> + struct hci_uart *hu = qca->hu;
>>>>> + struct qca_memdump_data *qca_memdump = qca->qca_memdump;
>>>>> + char *memdump_buf = qca_memdump->memdump_buf_tail;
>>>>> +
>>>>> + bt_dev_err(hu->hdev, "clearing allocated memory due to memdump timeout");
>>>>> + kfree(memdump_buf);
>>>>> + kfree(qca_memdump);
>>>>> + qca->memdump_state = QCA_MEMDUMP_TIMEOUT;
>>>>> + del_timer(&qca->memdump_timer);
>>>>> + cancel_work_sync(&qca->ctrl_memdump_evt);
>>>>> +}
>>>>> +
>>>>> /* Initialize protocol */
>>>>> static int qca_open(struct hci_uart *hu)
>>>>> {
>>>>> @@ -461,6 +520,7 @@ static int qca_open(struct hci_uart *hu)
>>>>> skb_queue_head_init(&qca->txq);
>>>>> skb_queue_head_init(&qca->tx_wait_q);
>>>>> + skb_queue_head_init(&qca->rx_memdump_q);
>>>>> spin_lock_init(&qca->hci_ibs_lock);
>>>>> qca->workqueue = alloc_ordered_workqueue("qca_wq", 0);
>>>>> if (!qca->workqueue) {
>>>>> @@ -473,6 +533,7 @@ static int qca_open(struct hci_uart *hu)
>>>>> INIT_WORK(&qca->ws_awake_device, qca_wq_awake_device);
>>>>> INIT_WORK(&qca->ws_rx_vote_off, qca_wq_serial_rx_clock_vote_off);
>>>>> INIT_WORK(&qca->ws_tx_vote_off, qca_wq_serial_tx_clock_vote_off);
>>>>> + INIT_WORK(&qca->ctrl_memdump_evt, qca_controller_memdump);
>>>>> qca->hu = hu;
>>>>> @@ -500,7 +561,7 @@ static int qca_open(struct hci_uart *hu)
>>>>> qca->tx_votes_off = 0;
>>>>> qca->rx_votes_on = 0;
>>>>> qca->rx_votes_off = 0;
>>>>> -
>>>>> + qca->memdump_state = QCA_MEMDUMP_IDLE;
>>>>> hu->priv = qca;
>>>>> if (hu->serdev) {
>>>>> @@ -528,6 +589,9 @@ static int qca_open(struct hci_uart *hu)
>>>>> timer_setup(&qca->tx_idle_timer, hci_ibs_tx_idle_timeout, 0);
>>>>> qca->tx_idle_delay = IBS_TX_IDLE_TIMEOUT_MS;
>>>>> + timer_setup(&qca->memdump_timer, hci_memdump_timeout, 0);
>>>>> + qca->memdump_delay = MEMDUMP_COLLECTION_TIMEOUT_MS;
>>>>> +
>>>>> BT_DBG("HCI_UART_QCA open, tx_idle_delay=%u, wake_retrans=%u",
>>>>> qca->tx_idle_delay, qca->wake_retrans);
>>>>> @@ -605,8 +669,10 @@ static int qca_close(struct hci_uart *hu)
>>>>> skb_queue_purge(&qca->tx_wait_q);
>>>>> skb_queue_purge(&qca->txq);
>>>>> + skb_queue_purge(&qca->rx_memdump_q);
>>>>> del_timer(&qca->tx_idle_timer);
>>>>> del_timer(&qca->wake_retrans_timer);
>>>>> + del_timer(&qca->memdump_timer);
>>>>> destroy_workqueue(qca->workqueue);
>>>>> qca->hu = NULL;
>>>>> @@ -866,6 +932,141 @@ static int qca_recv_acl_data(struct hci_dev *hdev, struct sk_buff *skb)
>>>>> return hci_recv_frame(hdev, skb);
>>>>> }
>>>>> +static void qca_controller_memdump(struct work_struct *work)
>>>>> +{
>>>>> + struct qca_data *qca = container_of(work, struct qca_data,
>>>>> + ctrl_memdump_evt);
>>>>> + struct hci_uart *hu = qca->hu;
>>>>> + struct sk_buff *skb;
>>>>> + struct qca_memdump_event_hdr *cmd_hdr;
>>>>> + struct qca_memdump_data *qca_memdump = qca->qca_memdump;
>>>>> + struct qca_dump_size *dump;
>>>>> + char *memdump_buf;
>>>>> + char nullBuff[QCA_DUMP_PACKET_SIZE] = { 0 };
>>>>> + u16 opcode, seq_no;
>>>>> + u32 dump_size;
>>>>> +
>>>>> + while ((skb = skb_dequeue(&qca->rx_memdump_q))) {
>>>>> +
>>>>> + if (!qca_memdump) {
>>>>> + qca_memdump = kzalloc(sizeof(struct qca_memdump_data),
>>>>> + GFP_ATOMIC);
>>>>> + if (!qca_memdump)
>>>>> + return;
>>>>> +
>>>>> + qca->qca_memdump = qca_memdump;
>>>>> + }
>>>>> +
>>>>> + qca->memdump_state = QCA_MEMDUMP_COLLECTING;
>>>>> + cmd_hdr = (void *) skb->data;
>>>>> + opcode = __le16_to_cpu(cmd_hdr->opcode);
>>>>> + seq_no = __le16_to_cpu(cmd_hdr->seq_no);
>>>>> + skb_pull(skb, sizeof(struct qca_memdump_event_hdr));
>>>>> +
>>>>> + if (!seq_no) {
>>>>> +
>>>>> + /* This is the first frame of memdump packet from
>>>>> + * the controller, Disable IBS to recevie dump
>>>>> + * with out any interruption, ideally time required for
>>>>> + * the controller to send the dump is 8 seconds. let us
>>>>> + * start timer to handle this asynchronous activity.
>>>>> + */
>>>>> + clear_bit(STATE_IN_BAND_SLEEP_ENABLED, &qca->flags);
>>>>> +
>>>>> + dump = (void *) skb->data;
>>>>> + dump_size = __le32_to_cpu(dump->dump_size);
>>>>> + if (!(dump_size)) {
>>>>> + bt_dev_err(hu->hdev, "QCA invalid memdump size");
>>>>> + kfree_skb(skb);
>>>>> + return;
>>>>> + }
>>>>> +
>>>>> + bt_dev_info(hu->hdev, "QCA: collecting memdump started"
>>>>> + "of size:%u", dump_size);
>>>>> + mod_timer(&qca->memdump_timer, (jiffies +
>>>>> + msecs_to_jiffies(qca->memdump_delay)));
>>>>> +
>>>>> + skb_pull(skb, sizeof(dump_size));
>>>>> + memdump_buf = vmalloc(dump_size);
>>>>> + qca_memdump->memdump_buf_head = memdump_buf;
>>>>> + qca_memdump->memdump_buf_tail = memdump_buf;
>>>>> + }
>>>>> +
>>>>> + memdump_buf = qca_memdump->memdump_buf_tail;
>>>>> +
>>>>> + /* If sequence no 0 is missed then there is no point in
>>>>> + * accepting the other sequences.
>>>>> + */
>>>>> + if (!memdump_buf) {
>>>>> + bt_dev_err(hu->hdev, "QCA: Discarding other packets");
>>>>> + kfree(qca_memdump);
>>>>> + kfree_skb(skb);
>>>>> + qca->qca_memdump = NULL;
>>>>> + return;
>>>>> + }
>>>>> +
>>>>> + /* There could be chance of missing some packets from
>>>>> + * the controller. In such cases let us store the dummy
>>>>> + * packets in the buffer.
>>>>> + */
>>>>> + while ((seq_no > qca_memdump->current_seq_no + 1) &&
>>>>> + seq_no != QCA_LAST_SEQUENCE_NUM) {
>>>>> + bt_dev_err(hu->hdev, "QCA controller missed packet:%d",
>>>>> + qca_memdump->current_seq_no);
>>>>> + memcpy(memdump_buf, nullBuff, QCA_DUMP_PACKET_SIZE);
>>>>> + memdump_buf = memdump_buf + QCA_DUMP_PACKET_SIZE;
>>>>> + qca_memdump->received_dump += QCA_DUMP_PACKET_SIZE;
>>>>> + qca_memdump->current_seq_no++;
>>>>> + }
>>>>> +
>>>>> + memcpy(memdump_buf, (unsigned char *) skb->data, skb->len);
>>>>> + memdump_buf = memdump_buf + skb->len;
>>>>> + qca_memdump->memdump_buf_tail = memdump_buf;
>>>>> + qca_memdump->current_seq_no = seq_no + 1;
>>>>> + qca_memdump->received_dump += skb->len;
>>>>> + qca->qca_memdump = qca_memdump;
>>>>> + kfree_skb(skb);
>>>>> + if (seq_no == QCA_LAST_SEQUENCE_NUM) {
>>>>> + bt_dev_info(hu->hdev, "QCA writing crash dump of size %d bytes",
>>>>> + qca_memdump->received_dump);
>>>>> + memdump_buf = qca_memdump->memdump_buf_head;
>>>>> + dev_coredumpv(&hu->serdev->dev, memdump_buf,
>>>>> + qca_memdump->received_dump, GFP_KERNEL);
>>>>> + // Revisit for free(memdump) if needed.
>>>>> + del_timer(&qca->memdump_timer);
>>>>> + kfree(qca->qca_memdump);
>>>>> + qca->qca_memdump = NULL;
>>>>> + qca->memdump_state = QCA_MEMDUMP_COLLECTED;
>>>>> + }
>>>>> + }
>>>>> +
>>>>> +}
>>>>> +
>>>>> +int qca_controller_memdump_event(struct hci_dev *hdev, struct sk_buff *skb)
>>>>> +{
>>>>> + struct hci_uart *hu = hci_get_drvdata(hdev);
>>>>> + struct qca_data *qca = hu->priv;
>>>>> +
>>>>> + skb_queue_tail(&qca->rx_memdump_q, skb);
>>>>> + queue_work(qca->workqueue, &qca->ctrl_memdump_evt);
>>>>> +
>>>>> + return 0;
>>>>> +}
>>>>> +
>>>>> +static int qca_recv_event_data(struct hci_dev *hdev, struct sk_buff *skb)
>>>>> +{
>>>>> + /* We receive chip memory dump as an event packet, With a dedicated
>>>>> + * handler followed by a hardware error event. When this event is
>>>>> + * received we store dump into a file before closing hci. This
>>>>> + * dump will help in triaging the issues.
>>>>> + */
>>>>> + if ((skb->data[0] == HCI_VENDOR_PKT) &&
>>>>> + (get_unaligned_be16((skb->data) + 2) == QCA_SSR_DUMP_HANDLE))
>>>> The (skb->data) is pointless, just do skb->data.
>>> [Bala]: will update.
>>>>> + return qca_controller_memdump_event(hdev, skb);
>>>>> +
>>>>> + return hci_recv_frame(hdev, skb);
>>>>> +}
>>>>> +
>>>>> #define QCA_IBS_SLEEP_IND_EVENT \
>>>>> .type = HCI_IBS_SLEEP_IND, \
>>>>> .hlen = 0, \
>>>>> @@ -888,12 +1089,12 @@ static int qca_recv_acl_data(struct hci_dev *hdev, struct sk_buff *skb)
>>>>> .maxlen = HCI_MAX_IBS_SIZE
>>>>> static const struct h4_recv_pkt qca_recv_pkts[] = {
>>>>> - { H4_RECV_ACL, .recv = qca_recv_acl_data },
>>>>> - { H4_RECV_SCO, .recv = hci_recv_frame },
>>>>> - { H4_RECV_EVENT, .recv = hci_recv_frame },
>>>>> - { QCA_IBS_WAKE_IND_EVENT, .recv = qca_ibs_wake_ind },
>>>>> - { QCA_IBS_WAKE_ACK_EVENT, .recv = qca_ibs_wake_ack },
>>>>> - { QCA_IBS_SLEEP_IND_EVENT, .recv = qca_ibs_sleep_ind },
>>>>> + { H4_RECV_ACL, .recv = qca_recv_acl_data },
>>>>> + { H4_RECV_SCO, .recv = hci_recv_frame },
>>>>> + { H4_RECV_EVENT, .recv = qca_recv_event_data },
>>>> call it qca_recv_event and don't realign the whole table.
>>> [Bala]: will update.
>>>>> + { QCA_IBS_WAKE_IND_EVENT, .recv = qca_ibs_wake_ind },
>>>>> + { QCA_IBS_WAKE_ACK_EVENT, .recv = qca_ibs_wake_ack },
>>>>> + { QCA_IBS_SLEEP_IND_EVENT, .recv = qca_ibs_sleep_ind },
>>>>> };
>>>>> static int qca_recv(struct hci_uart *hu, const void *data, int count)
>>>>> @@ -1114,6 +1315,68 @@ static int qca_set_speed(struct hci_uart *hu, enum qca_speed_type speed_type)
>>>>> return 0;
>>>>> }
>>>>> +static int qca_send_crashbuffer(struct hci_uart *hu)
>>>>> +{
>>>>> + struct qca_data *qca = hu->priv;
>>>>> + struct sk_buff *skb;
>>>>> + unsigned char buf[QCA_CRASHBYTE_PACKET_LEN];
>>>>> +
>>>>> + bt_dev_dbg(hu->hdev, "sending soc crash buffer to controller");
>>>>> +
>>>>> + /* We forcefully crash the controller, by sending 0xfb byte for
>>>>> + * 1024 times. We also might have chance of losing data, To be
>>>>> + * on safer side we send 1100 bytes to the SoC.
>>>>> + */
>>>>> + memset(buf, QCA_MEMDUMP_BYTE, QCA_CRASHBYTE_PACKET_LEN);
>>>>> +
>>>>> + skb = bt_skb_alloc(QCA_CRASHBYTE_PACKET_LEN, GFP_KERNEL);
>>>>> + if (!skb) {
>>>>> + bt_dev_err(hu->hdev, "Failed to allocate memory for skb packet");
>>>>> + return -ENOMEM;
>>>>> + }
>>>>> +
>>>>> + skb_put_data(skb, buf, QCA_CRASHBYTE_PACKET_LEN);
>>>>> + hci_skb_pkt_type(skb) = HCI_COMMAND_PKT;
>>>>> +
>>>>> + skb_queue_tail(&qca->txq, skb);
>>>>> + hci_uart_tx_wakeup(hu);
>>>>> +
>>>>> + return 0;
>>>>> +}
>>>>> +
>>>>> +static void qca_hw_error(struct hci_dev *hdev, u8 code)
>>>>> +{
>>>>> + struct hci_uart *hu = hci_get_drvdata(hdev);
>>>>> + struct qca_data *qca = hu->priv;
>>>>> +
>>>>> + bt_dev_info(hdev, "mem_dump_status: %d", qca->memdump_state);
>>>>> +
>>>>> + if (qca->memdump_state == QCA_MEMDUMP_IDLE) {
>>>>> + /* If hardware error event received for other than QCA
>>>>> + * soc memory dump event, then we need to crash the SOC
>>>>> + * and wait here for 8 seconds to get the dump packets.
>>>>> + * This will block main thread to be on hold until we
>>>>> + * collect dump.
>>>>> + */
>>>>> + mod_timer(&qca->memdump_timer,
>>>>> + (jiffies + msecs_to_jiffies(qca->memdump_delay)));
>>>> Why a timer that then ends up in interrupt context?
>>> [Bala]: some times we only receive hardware error from the chip, so we are sending an special buffer to request the
>>> chip for memory dump. we are using an timer to check whether the data memdump is collected. if the timer
>>> over flows we are cleaning up all the assigned memory and unblock the main thread,
>>> in short this timer is a watch dog timer for the memory dump collection.
>> I saw that you used a bunch of timers actually. My question is why are
>> these not delayed_wq instead? I wonder if we really want to keep using
>> timers and handling interrupt context locking if we could move
>> everything to wq instead.
>
> [Bala]: Let me brief you the requirement.
> This patch is used to collect the memory dump received from the chip and store it into a file.
> We receive chip memory dump in two cases
> 1. When chip goes into the bad state it sends the dump followed by and hardware error event.
> 2. Some time when we send some garbage or un recognized command to chip.
> it will respond with a hardware error event. So we send an 0xfb bytes to the chip requesting it to send the memory dump.
>
> In both cases, chip will go into the bad state once it sends the dump. so we need to turn OFF and ON chip and perform the init procedure.
> So keeping the above cases in the view, we register an handle for hardware error event. So that in both the cases hw error routine will execute.
>
> As the dump as some specific headers we will queue the received data into work queue.
> We are blocking the main thread until the total dump is stored into the file.
> Here is the answer for the question, yes we check the status of the work queue but for handling case 2 we require timers.
> But let us assume the wq is taking more time than expected. Then we also need a timer.
> we are using timer so that we will not block the main thread indefinitely.
> They are some cases where when we request a memory dump, after some packet sent by the chip.
> it may go into a bad state where it will not pump the remaining dump, so we are using a timer to unblock the main thread.
> so during timeout, we are restarting the flags to unblock the main thread.
>
>
>>>>> + qca_send_crashbuffer(hu);
>>>>> +
>>>>> + while (qca->memdump_state != QCA_MEMDUMP_COLLECTED &&
>>>>> + qca->memdump_state != QCA_MEMDUMP_TIMEOUT)
>>>>> + ;
>>>> What is this? Busy loop? I rather not do that.
>>> [Bala]: this busy required to collected the dump from the chip before we close an reopen the hci.
>>> >> + } else if (qca->memdump_state == QCA_MEMDUMP_COLLECTING) {
>> Why not use some wakeup handling here. I am really against any kind of
>> busy loops in a driver.
> [Bala]: this busy loop is require. pls refer my comments to the above query.
> this will help in mainly in case 2, where we will block the main thread until we have dump collected.
>
> let us assume that we received an hardware error event, hw error routine we execute which sends an
> special byte to the chip requesting for memory dump. it starts sending the dump, but we move forward and turn off the
> chip so we will miss the dump. so here the busy loop is to wait until we have dump.
> but the we are not waiting indefinitely we have timer to unblock them.
I do not see how any of this is correct. Can you not use some wakeup helper like everybody else does. I also do not see how these two threads are correctly protected. It looks really hackish to me.
Regards
Marcel