Re: [PATCH v2 1/5] bus: mhi: core: Handle syserr during power_up

From: Jeffrey Hugo
Date: Fri Apr 10 2020 - 17:40:25 EST

On 4/10/2020 2:37 PM, Bhaumik Vasav Bhatt wrote:
Hi Jeff,

We will always have the mhi_intvec_handler registered and trigger your wake_up state event when you write MHI RESET. BHI INTVEC IRQ using mhi_cntrl->irq[0] is _not_ unregistered once you enter AMSS EE.

I understand it is not unregistered. However mhi_cntrl->irq[0] may be reserved for BHI, and thus only exercised by PBL EE. Where as, mhi_cntrl->irq[1..N] may be only exercised by AMSS EE. mhi_intvec_handler is not called in response to mhi_cntrl->irq[1..N].

Additionally, I re-reviewed the MHI spec, and I don't see where the spec requires the device to issue an interrupt upon completion of the RESET request.

Under section 3.5, step 11 states -

"The host must poll for the value of the RESET bit to detect the completion of the reset procedure by the device (RESET is set to 0)."

So, by this, my proposed solution appears to be spec compliant, where as what Hemant proposed is not.


So, your below assumption is not true:
>>>So, if we are in the PBL EE, we would expect to see the BHI interrupt, but if we are in the AMSS EE, we would expect to see a MHI interrupt.

At the start of mhi_async_power_up(), you've already registered for the BHI interrupt as we do setup for IRQ and it is only unregistered from power down if power up on the same cycle was a success.

You seem to have misunderstood my point. If the BHI irq is only for BHI activity, which is activity restricted to the PBL EE, and the MHI interrupt(s) are restricted to MHI activity, which for the purposes of this discussion only occur in the AMSS EE, then my assumption is correct. When the device is in PBL EE, we should only observe BHI irqs, and when the device is in AMSS EE, we should only observe MHI irqs.

This is a statement of what IRQ lines the device is raising, and not a statement of what handlers the host has, or has not registered.

Again, if the BHI irq is only generated in the PBL EE, and we rely on the BHI irq for "sensing" the state_event - we will never see the state_event in the AMSS EE, unless the same IRQ line is used for both MHI and BHI (which is only a select set of usecases, and not universal).


On 4/10/20 8:03 AM, Jeffrey Hugo wrote:
On 4/9/2020 6:55 PM, Hemant Kumar wrote:

On 4/7/20 9:50 AM, Jeffrey Hugo wrote:
The MHI device may be in the syserr state when we attempt to init it in
power_up(). Since we have no local state, the handling is simple -
reset the device and wait for it to transition out of the reset state.

Signed-off-by: Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx>
---
 drivers/bus/mhi/core/pm.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
index 52690cb..3285c9e 100644
--- a/drivers/bus/mhi/core/pm.c
+++ b/drivers/bus/mhi/core/pm.c
@@ -9,6 +9,7 @@
 #include <linux/dma-direction.h>
 #include <linux/dma-mapping.h>
 #include <linux/interrupt.h>
+#include <linux/iopoll.h>
 #include <linux/list.h>
 #include <linux/mhi.h>
 #include <linux/module.h>
@@ -760,6 +761,7 @@ static void mhi_deassert_dev_wake(struct mhi_controller *mhi_cntrl,
 int mhi_async_power_up(struct mhi_controller *mhi_cntrl)
 {
+ÂÂÂ enum mhi_state state;
ÂÂÂÂÂ enum mhi_ee_type current_ee;
ÂÂÂÂÂ enum dev_st_transition next_state;
ÂÂÂÂÂ struct device *dev = &mhi_cntrl->mhi_dev->dev;
@@ -829,6 +831,24 @@ int mhi_async_power_up(struct mhi_controller *mhi_cntrl)
ÂÂÂÂÂÂÂÂÂ goto error_bhi_offset;
ÂÂÂÂÂ }
+ÂÂÂ state = mhi_get_mhi_state(mhi_cntrl);
+ÂÂÂ if (state == MHI_STATE_SYS_ERR) {
+ÂÂÂÂÂÂÂ mhi_set_mhi_state(mhi_cntrl, MHI_STATE_RESET);
+ÂÂÂÂÂÂÂ ret = readl_poll_timeout(mhi_cntrl->regs + MHICTRL, val,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ !(val & MHICTRL_RESET_MASK), 1000,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ mhi_cntrl->timeout_ms * 1000);
can we use this instead of polling because MSI is configures and int_vec handler is registered

ÂÂÂÂ wait_event_timeout(mhi_cntrl->state_event,
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ MHI_PM_IN_FATAL_STATE(mhi_cntrl->pm_state) ||
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ mhi_read_reg_field(mhi_cntrl, base, MHICTRL,
ÂÂÂÂ ÂÂÂ ÂÂÂ ÂÂÂ ÂÂÂ ÂÂÂÂÂ MHICTRL_RESET_MASK,
ÂÂÂÂ ÂÂÂ ÂÂÂ ÂÂÂ ÂÂÂ ÂÂÂÂÂ MHICTRL_RESET_SHIFT, &reset) || !reset ,
ÂÂÂÂ ÂÂÂ ÂÂÂ ÂÂ msecs_to_jiffies(mhi_cntrl->timeout_ms));

1) In case of MHI_PM_IN_FATAL_STATE we would not be accessing MHI reg
2) Consistent with current MHI driver code.

I'm not sure this works in the way you intend.

state_event is linked to the intvec, which is the BHI interrupt. I don't see that the state_event is triggered in the MHI interrupt path (mhi_irq_handler). So, if we are in the PBL EE, we would expect to see the BHI interrupt, but if we are in the AMSS EE, we would expect to see a MHI interrupt.

Now, for my concerned usecase, those two interrupts happen to be the same interrupt, so both will get triggered, but I don't expect that to be the same for all usecases.

So, with the solution I propose, we exit the wait (poll loop) as soon as we see the register change values.

With the solution you propose, if we only get the MHI interrupt, we'll have to wait out the entire timeout value, and then check the register. In this scenario, we are almost guaranteed to wait for longer than necessary.

Did I miss something?

+ÂÂÂÂÂÂÂ if (ret) {
+ÂÂÂÂÂÂÂÂÂÂÂ dev_info(dev, "Failed to reset MHI due to syserr state\n");
+ÂÂÂÂÂÂÂÂÂÂÂ goto error_bhi_offset;
+ÂÂÂÂÂÂÂ }
+
+ÂÂÂÂÂÂÂ /*
+ÂÂÂÂÂÂÂÂ * device cleares INTVEC as part of RESET processing,
+ÂÂÂÂÂÂÂÂ * re-program it
+ÂÂÂÂÂÂÂÂ */
+ÂÂÂÂÂÂÂ mhi_write_reg(mhi_cntrl, mhi_cntrl->bhi, BHI_INTVEC, 0);
+ÂÂÂ }
+
ÂÂÂÂÂ /* Transition to next state */
ÂÂÂÂÂ next_state = MHI_IN_PBL(current_ee) ?
ÂÂÂÂÂÂÂÂÂ DEV_ST_TRANSITION_PBL : DEV_ST_TRANSITION_READY;





--
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.