Re: [RFC PATCH v6] media: add v4l2 subdev driver for S5K4ECGX sensor

[Francesco Lavra <francescolavra.fl@gmail.com>]

Hi,

On 09/10/2012 05:04 PM, Sylwester Nawrocki wrote:
> Hi,
> 
> On 09/09/2012 06:01 PM, Francesco Lavra wrote:
>>> +static int s5k4ecgx_load_firmware(struct v4l2_subdev *sd)
>>> +{
>>> +	const struct firmware *fw;
>>> +	int err, i, regs_num;
>>> +	struct i2c_client *client = v4l2_get_subdevdata(sd);
>>> +	u16 val;
>>> +	u32 addr, crc, crc_file, addr_inc = 0;
>>> +
>>> +	err = request_firmware(&fw, S5K4ECGX_FIRMWARE, sd->v4l2_dev->dev);
>>> +	if (err) {
>>> +		v4l2_err(sd, "Failed to read firmware %s\n", S5K4ECGX_FIRMWARE);
>>> +		return err;
>>> +	}
>>> +	regs_num = *(u32 *)(fw->data);
>>> +	v4l2_dbg(3, debug, sd, "FW: %s size %d register sets %d\n",
>>> +		 S5K4ECGX_FIRMWARE, fw->size, regs_num);
>>> +	regs_num++; /* Add header */
>>> +	if (fw->size != regs_num * FW_RECORD_SIZE + FW_CRC_SIZE) {
>>> +		err = -EINVAL;
>>> +		goto fw_out;
>>> +	}
>>> +	crc_file = *(u32 *)(fw->data + regs_num * FW_RECORD_SIZE);
>>
>> Depending on the value of regs_num, this may result in unaligned access
> 
> Thanks for the catch. I think it is not the only place where unaligned
> issues are possible. Since the data records are 4-byte address + 2-byte
> value there is also an issue with reading the address entries. Assuming
> fw->data is aligned to at least 2-bytes (not quite sure if we can assume
> that) there should be no problem with reading 2-byte register values.

I'm not sure 2-byte alignment can be safely assumed, either.

> We could change the data types of the register values from u16 to u32,
> wasting some memory (there is approximately 3 000 records), so there is
> no other data types in the file structure than u32. Or use a patch as
> below. Not sure what's better.

I prefer the approach of your patch below, but I would use get_unaligned
to get the 2-byte values, too. Also there are another couple of
glitches, see below.

> 
> 8<---------------------------------------------------------------------
> From a970480b99bdb74e2bf48e1a321724231e6516a0 Mon Sep 17 00:00:00 2001
> From: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
> Date: Sun, 9 Sep 2012 19:56:31 +0200
> Subject: [PATCH] s5k4ecgx: Fix unaligned access issues
> 
> Signed-off-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
> ---
>  drivers/media/i2c/s5k4ecgx.c |   16 ++++++++++++----
>  1 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/i2c/s5k4ecgx.c b/drivers/media/i2c/s5k4ecgx.c
> index 0ef0b7d..4c6439a 100644
> --- a/drivers/media/i2c/s5k4ecgx.c
> +++ b/drivers/media/i2c/s5k4ecgx.c
> @@ -24,6 +24,7 @@
>  #include <linux/module.h>
>  #include <linux/regulator/consumer.h>
>  #include <linux/slab.h>
> +#include <asm/unaligned.h>
> 
>  #include <media/media-entity.h>
>  #include <media/s5k4ecgx.h>
> @@ -331,6 +332,7 @@ static int s5k4ecgx_load_firmware(struct v4l2_subdev *sd)
>  	const struct firmware *fw;
>  	int err, i, regs_num;
>  	u32 addr, crc, crc_file, addr_inc = 0;
> +	const u8 *ptr;
>  	u16 val;
> 
>  	err = request_firmware(&fw, S5K4ECGX_FIRMWARE, sd->v4l2_dev->dev);
> @@ -338,7 +340,7 @@ static int s5k4ecgx_load_firmware(struct v4l2_subdev *sd)
>  		v4l2_err(sd, "Failed to read firmware %s\n", S5K4ECGX_FIRMWARE);
>  		return err;
>  	}
> -	regs_num = le32_to_cpu(*(u32 *)fw->data);
> +	regs_num = le32_to_cpu(get_unaligned((__le32 *)fw->data));
> 
>  	v4l2_dbg(3, debug, sd, "FW: %s size %d register sets %d\n",
>  		 S5K4ECGX_FIRMWARE, fw->size, regs_num);
> @@ -349,7 +351,8 @@ static int s5k4ecgx_load_firmware(struct v4l2_subdev *sd)
>  		goto fw_out;
>  	}
> 
> -	crc_file = *(u32 *)(fw->data + regs_num * FW_RECORD_SIZE);
> +	memcpy(&crc_file, fw->data + regs_num * FW_RECORD_SIZE, sizeof(u32));

crc_file should be converted from little endian to native endian.

> +
>  	crc = crc32_le(~0, fw->data, regs_num * FW_RECORD_SIZE);
>  	if (crc != crc_file) {
>  		v4l2_err(sd, "FW: invalid crc (%#x:%#x)\n", crc, crc_file);
> @@ -357,9 +360,14 @@ static int s5k4ecgx_load_firmware(struct v4l2_subdev *sd)
>  		goto fw_out;
>  	}
> 
> +	ptr = fw->data + FW_RECORD_SIZE;
> +
>  	for (i = 1; i < regs_num; i++) {
> -		addr = le32_to_cpu(*(u32 *)(fw->data + i * FW_RECORD_SIZE));
> -		val = le16_to_cpu(*(u16 *)(fw->data + i * FW_RECORD_SIZE + 4));
> +		addr = le32_to_cpu(get_unaligned((__le32 *)ptr));
> +		ptr += 4;
> +		val = le16_to_cpu(*(__le16 *)ptr);
> +		ptr += FW_RECORD_SIZE;

ptr is being incremented by (4 + FW_RECORD_SIZE) bytes at each iteration.

> +
>  		if (addr - addr_inc != 2)
>  			err = s5k4ecgx_write(client, addr, val);
>  		else

--
Francesco