Re: [PATCH V22 2/3] misc: dcc: Add driver support for Data Capture and Compare unit(DCC)

[Greg Kroah-Hartman]

On Tue, Apr 18, 2023 at 08:52:36PM +0530, Souradeep Chowdhury wrote:
> The DCC is a DMA Engine designed to capture and store data during system
> crash or software triggers. The DCC operates based on user inputs via
> the debugfs interface. The user gives addresses as inputs and these
> addresses are stored in the dcc sram. In case of a system crash or a
> manual software trigger by the user through the debugfs interface, the
> dcc captures and stores the values at these addresses. This patch
> contains the driver which has all the methods pertaining to the debugfs
> interface, auxiliary functions to support all the four fundamental
> operations of dcc namely read, write, read/modify/write and loop. The
> probe method here instantiates all the resources necessary for dcc to
> operate mainly the dedicated dcc sram where it stores the values. The
> DCC driver can be used for debugging purposes without going for a reboot
> since it can perform software triggers as well based on user inputs.
> 
> Also add the documentation for debugfs entries which explains the
> functionalities of each debugfs file that has been created for dcc.

I see no documentation entries in this commit :(

> The following is the justification of using debugfs interface over the
> other alternatives like sysfs/ioctls
> 
> i) As can be seen from the debugfs attribute descriptions, some of the
> debugfs attribute files here contains multiple arguments which needs to
> be accepted from the user. This goes against the design style of sysfs.
> 
> ii) The user input patterns have been made simple and convenient in this
> case with the use of debugfs interface as user doesn't need to shuffle
> between different files to execute one instruction as was the case on
> using other alternatives.

Why do you have debugfs and also a misc device?  How are they related?
Why both?  Why not just one?  What userspace tools are going to use
either of these interfaces and where are they published to show how this
all was tested?

> Signed-off-by: Souradeep Chowdhury <quic_schowdhu@xxxxxxxxxxx>
> Reviewed-by: Alex Elder <elder@xxxxxxxxxx>
> ---
>  drivers/misc/Kconfig  |    8 +
>  drivers/misc/Makefile |    1 +
>  drivers/misc/dcc.c    | 1300 +++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 1309 insertions(+)
>  create mode 100644 drivers/misc/dcc.c
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 433aa41..e2bc652 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -276,6 +276,14 @@ config QCOM_COINCELL
>  	  to maintain PMIC register and RTC state in the absence of
>  	  external power.
>  
> +config QCOM_DCC
> +	tristate "Qualcomm Technologies, Inc. Data Capture and Compare(DCC) engine driver"
> +	depends on ARCH_QCOM || COMPILE_TEST
> +	help
> +	  This option enables driver for Data Capture and Compare engine. DCC
> +	  driver provides interface to configure DCC block and read back
> +	  captured data from DCC's internal SRAM.


What is the module name?

> +
>  config QCOM_FASTRPC
>  	tristate "Qualcomm FastRPC"
>  	depends on ARCH_QCOM || COMPILE_TEST
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index 56de439..6fa8efa 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -16,6 +16,7 @@ obj-$(CONFIG_TIFM_CORE)       	+= tifm_core.o
>  obj-$(CONFIG_TIFM_7XX1)       	+= tifm_7xx1.o
>  obj-$(CONFIG_PHANTOM)		+= phantom.o
>  obj-$(CONFIG_QCOM_COINCELL)	+= qcom-coincell.o
> +obj-$(CONFIG_QCOM_DCC)		+= dcc.o

Why such a generic name?  Shouldn't it be qcom-dcc?



>  obj-$(CONFIG_QCOM_FASTRPC)	+= fastrpc.o
>  obj-$(CONFIG_SENSORS_BH1770)	+= bh1770glc.o
>  obj-$(CONFIG_SENSORS_APDS990X)	+= apds990x.o
> diff --git a/drivers/misc/dcc.c b/drivers/misc/dcc.c
> new file mode 100644
> index 0000000..7231ed9
> --- /dev/null
> +++ b/drivers/misc/dcc.c
> @@ -0,0 +1,1300 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2015-2021, The Linux Foundation. All rights reserved.
> + * Copyright (c) 2023, Qualcomm Innovation Center, Inc. All rights reserved.

No work happened on this code in 2022?  All 22 of these entries were
only in 2021 and 2023?

> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/bitops.h>
> +#include <linux/debugfs.h>
> +#include <linux/delay.h>
> +#include <linux/fs.h>
> +#include <linux/io.h>
> +#include <linux/iopoll.h>
> +#include <linux/miscdevice.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +
> +#define STATUS_READY_TIMEOUT		5000  /* microseconds */
> +
> +/* DCC registers */
> +#define DCC_HW_INFO			0x04
> +#define DCC_LL_NUM_INFO			0x10
> +#define DCC_STATUS(vers)		((vers) == 1 ? 0x0c : 0x1c)

Why isn't this just an inline function?

> +#define DCC_LL_LOCK			0x00
> +#define DCC_LL_CFG			0x04
> +#define DCC_LL_BASE			0x08
> +#define DCC_FD_BASE			0x0c
> +#define DCC_LL_TIMEOUT			0x10
> +#define DCC_LL_INT_ENABLE		0x18
> +#define DCC_LL_INT_STATUS		0x1c
> +#define DCC_LL_SW_TRIGGER		0x2c
> +#define DCC_LL_BUS_ACCESS_STATUS	0x30
> +
> +/* Default value used if a bit 6 in the HW_INFO register is set. */
> +#define DCC_FIX_LOOP_OFFSET		16
> +
> +/* Mask to find version info from HW_Info register */
> +#define DCC_VER_INFO_MASK		BIT(9)
> +
> +#define MAX_DCC_OFFSET			GENMASK(9, 2)
> +#define MAX_DCC_LEN			GENMASK(6, 0)
> +#define MAX_LOOP_CNT			GENMASK(7, 0)
> +#define MAX_LOOP_ADDR			10
> +
> +#define DCC_ADDR_DESCRIPTOR		0x00
> +#define DCC_ADDR_LIMIT			27
> +#define DCC_WORD_SIZE			sizeof(u32)
> +#define DCC_ADDR_RANGE_MASK		GENMASK(31, 4)
> +#define DCC_LOOP_DESCRIPTOR		BIT(30)
> +#define DCC_RD_MOD_WR_DESCRIPTOR	BIT(31)
> +#define DCC_LINK_DESCRIPTOR		GENMASK(31, 30)
> +#define DCC_STATUS_MASK			GENMASK(1, 0)
> +#define DCC_LOCK_MASK			BIT(0)
> +#define DCC_LOOP_OFFSET_MASK		BIT(6)
> +#define DCC_TRIGGER_MASK		BIT(9)
> +
> +#define DCC_WRITE_MASK			BIT(15)
> +#define DCC_WRITE_OFF_MASK		GENMASK(7, 0)
> +#define DCC_WRITE_LEN_MASK		GENMASK(14, 8)
> +
> +#define DCC_READ_IND			0x00
> +#define DCC_WRITE_IND			(BIT(28))
> +
> +#define DCC_AHB_IND			0x00
> +#define DCC_APB_IND			BIT(29)
> +
> +#define DCC_MAX_LINK_LIST		8
> +
> +#define DCC_VER_MASK2			GENMASK(5, 0)
> +
> +#define DCC_SRAM_WORD_LENGTH		4
> +
> +#define DCC_RD_MOD_WR_ADDR              0xC105E
> +
> +enum dcc_descriptor_type {
> +	DCC_READ_TYPE,
> +	DCC_LOOP_TYPE,
> +	DCC_READ_WRITE_TYPE,
> +	DCC_WRITE_TYPE
> +};
> +
> +struct dcc_config_entry {
> +	u32				base;
> +	u32				offset;
> +	u32				len;
> +	u32				loop_cnt;
> +	u32				write_val;
> +	u32				mask;
> +	bool				apb_bus;
> +	enum dcc_descriptor_type	desc_type;
> +	struct list_head		list;
> +};

No documentation for this structure?

> +
> +/**
> + * struct dcc_drvdata - configuration information related to a dcc device
> + * @base:		Base Address of the dcc device
> + * @dev:		The device attached to the driver data
> + * @mutex:		Lock to protect access and manipulation of dcc_drvdata
> + * @ram_base:		Base address for the SRAM dedicated for the dcc device
> + * @ram_size:		Total size of the SRAM dedicated for the dcc device
> + * @ram_offset:		Offset to the SRAM dedicated for dcc device
> + * @mem_map_ver:	Memory map version of DCC hardware
> + * @ram_cfg:		Used for address limit calculation for dcc
> + * @ram_start:		Starting address of DCC SRAM
> + * @sram_dev:		Miscellaneous device equivalent of dcc SRAM
> + * @cfg_head:		Points to the head of the linked list of addresses
> + * @dbg_dir:		The dcc debugfs directory under which all the debugfs files are placed
> + * @nr_link_list:	Total number of linkedlists supported by the DCC configuration
> + * @loop_shift:		Loop offset bits range for the addresses
> + * @enable_bitmap:	Bitmap to capture the enabled status of each linked list of addresses
> + */
> +struct dcc_drvdata {
> +	void __iomem		*base;
> +	void __iomem            *ram_base;
> +	struct device		*dev;

Why do you need this back-pointer here?

> +	struct mutex		mutex;
> +	size_t			ram_size;
> +	size_t			ram_offset;
> +	int			mem_map_ver;
> +	unsigned int		ram_cfg;
> +	unsigned int		ram_start;
> +	struct miscdevice	sram_dev;

Wait, this is the struct device, right?  Or not?

> +	struct list_head	*cfg_head;
> +	struct dentry		*dbg_dir;

Why is this needed and not just looked up when necessary?

> +	size_t			nr_link_list;
> +	u8			loop_shift;
> +	unsigned long		*enable_bitmap;

So this is a list of bitmaps?  Why "unsigned long"?  Why not u64?

> +};
> +
> +struct dcc_cfg_attr {
> +	u32	addr;
> +	u32	prev_addr;
> +	u32	prev_off;
> +	u32	link;
> +	u32	sram_offset;
> +};
> +
> +struct dcc_cfg_loop_attr {
> +	u32	loop_cnt;
> +	u32	loop_len;
> +	u32	loop_off;
> +	bool    loop_start;
> +};
> +
> +static inline u32 dcc_list_offset(int version)
> +{
> +	return version == 1 ? 0x1c : version == 2 ? 0x2c : 0x34;
> +}

Ah, you do have an inline function for the above mentioned macro.
Please drop the macro.

And write this inline function out to be readable, single-level ?:
comments are impossible to read, let alone double-level ones.

Write code for people first, compilers second.  You gain nothing by
making this terse except to confuse people.

> +
> +static inline void dcc_list_writel(struct dcc_drvdata *drvdata,
> +				   u32 ll, u32 val, u32 off)
> +{
> +	u32 offset = dcc_list_offset(drvdata->mem_map_ver) + off;
> +
> +	writel(val, drvdata->base + ll * 0x80 + offset);

What is this magic 0x80 for?

> +}
> +
> +static inline u32 dcc_list_readl(struct dcc_drvdata *drvdata, u32 ll, u32 off)
> +{
> +	u32 offset = dcc_list_offset(drvdata->mem_map_ver) + off;
> +
> +	return readl(drvdata->base + ll * 0x80 + offset);

Again, where did 0x80 come from?

> +}
> +
> +static void dcc_sram_write_auto(struct dcc_drvdata *drvdata,
> +				u32 val, u32 *off)
> +{
> +	/* If the overflow condition is met increment the offset
> +	 * and return to indicate that overflow has occurred
> +	 */
> +	if (unlikely(*off > drvdata->ram_size - 4)) {
> +		*off += 4;
> +		return;

You didn't indicate anything here, all you did was succeed at the call,
the caller has no way of ever knowing this failed.

Why not return an error?

> +	}
> +
> +	writel(val, drvdata->ram_base + *off);
> +
> +	*off += 4;

See, same modification as your "error" above.

How was this tested?

> +static int dcc_emit_config(struct dcc_drvdata *drvdata, unsigned int curr_list)
> +{
> +	int ret;
> +	u32 total_len, pos;
> +	struct dcc_config_entry *entry;
> +	struct dcc_cfg_attr cfg;
> +	struct dcc_cfg_loop_attr cfg_loop;
> +
> +	memset(&cfg, 0, sizeof(cfg));
> +	memset(&cfg_loop, 0, sizeof(cfg_loop));

Why are these large structures on the stack?

And if on the stack, why not have the compiler initialize them to 0 for
you automatically?

I stopped reviewing here...

greg k-h