Re: [RFC] drm/bridge: megachips-stdpxxxx-ge-b850v3-fw: switch to drm_do_get_edid()

[Jani Nikula <jani.nikula@intel.com>]

On Fri, 01 Sep 2023, Jani Nikula <jani.nikula@intel.com> wrote:
> The driver was originally added in commit fcfa0ddc18ed ("drm/bridge:
> Drivers for megachips-stdpxxxx-ge-b850v3-fw (LVDS-DP++)"). I tried to
> look up the discussion, but didn't find anyone questioning the EDID
> reading part.
>
> Why does it not use drm_get_edid() or drm_do_get_edid()?
>
> I don't know where client->addr comes from, so I guess it could be
> different from DDC_ADDR, rendering drm_get_edid() unusable.
>
> There's also the comment:
>
> 	/* Yes, read the entire buffer, and do not skip the first
> 	 * EDID_LENGTH bytes.
> 	 */
>
> But again, there's not a word on *why*.
>
> Maybe we could just use drm_do_get_edid()? I'd like drivers to migrate
> away from their own EDID parsing and validity checks, including stop
> using drm_edid_block_valid(). (And long term switch to drm_edid_read(),
> struct drm_edid, and friends, but this is the first step.)
>
> Cc: Andrzej Hajda <andrzej.hajda@intel.com>
> Cc: Ian Ray <ian.ray@ge.com>
> Cc: Jernej Skrabec <jernej.skrabec@gmail.com>
> Cc: Jonas Karlman <jonas@kwiboo.se>
> Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
> Cc: Martin Donnelly <martin.donnelly@ge.com>
> Cc: Martyn Welch <martyn.welch@collabora.co.uk>
> Cc: Neil Armstrong <neil.armstrong@linaro.org>
> Cc: Peter Senna Tschudin <peter.senna@gmail.com>
> Cc: Robert Foss <rfoss@kernel.org>
> Cc: Yuan Can <yuancan@huawei.com>
> Cc: Zheyu Ma <zheyuma97@gmail.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>
> ---
>
> I haven't even tried to compile this, and I have no way to test
> this. Apologies for the long Cc list; I'm hoping someone could explain
> the existing code, and perhaps give this approach a spin.
> ---
>  .../bridge/megachips-stdpxxxx-ge-b850v3-fw.c  | 57 +++----------------
>  1 file changed, 9 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> index 460db3c8a08c..0d9eacf3d9b7 100644
> --- a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> +++ b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> @@ -65,12 +65,11 @@ struct ge_b850v3_lvds {
>  
>  static struct ge_b850v3_lvds *ge_b850v3_lvds_ptr;
>  
> -static u8 *stdp2690_get_edid(struct i2c_client *client)
> +static int stdp2690_read_block(void *context, u8 *buf, unsigned int block, size_t len)
>  {
> +	struct i2c_client *client = context;
>  	struct i2c_adapter *adapter = client->adapter;
> -	unsigned char start = 0x00;
> -	unsigned int total_size;
> -	u8 *block = kmalloc(EDID_LENGTH, GFP_KERNEL);
> +	unsigned char start = block * EDID_LENGTH;
>  
>  	struct i2c_msg msgs[] = {
>  		{
> @@ -81,53 +80,15 @@ static u8 *stdp2690_get_edid(struct i2c_client *client)
>  		}, {
>  			.addr	= client->addr,
>  			.flags	= I2C_M_RD,
> -			.len	= EDID_LENGTH,
> -			.buf	= block,
> +			.len	= len,
> +			.buf	= buf,
>  		}
>  	};
>  
> -	if (!block)
> -		return NULL;
> +	if (i2c_transfer(adapter, msgs, 2) != 2)
> +		return -1;
>  
> -	if (i2c_transfer(adapter, msgs, 2) != 2) {
> -		DRM_ERROR("Unable to read EDID.\n");
> -		goto err;
> -	}
> -
> -	if (!drm_edid_block_valid(block, 0, false, NULL)) {
> -		DRM_ERROR("Invalid EDID data\n");
> -		goto err;
> -	}
> -
> -	total_size = (block[EDID_EXT_BLOCK_CNT] + 1) * EDID_LENGTH;
> -	if (total_size > EDID_LENGTH) {
> -		kfree(block);
> -		block = kmalloc(total_size, GFP_KERNEL);
> -		if (!block)
> -			return NULL;
> -
> -		/* Yes, read the entire buffer, and do not skip the first
> -		 * EDID_LENGTH bytes.
> -		 */
> -		start = 0x00;
> -		msgs[1].len = total_size;
> -		msgs[1].buf = block;
> -
> -		if (i2c_transfer(adapter, msgs, 2) != 2) {
> -			DRM_ERROR("Unable to read EDID extension blocks.\n");
> -			goto err;
> -		}
> -		if (!drm_edid_block_valid(block, 1, false, NULL)) {
> -			DRM_ERROR("Invalid EDID data\n");
> -			goto err;
> -		}
> -	}
> -
> -	return block;
> -
> -err:
> -	kfree(block);
> -	return NULL;
> +	return 0;
>  }
>  
>  static struct edid *ge_b850v3_lvds_get_edid(struct drm_bridge *bridge,
> @@ -137,7 +98,7 @@ static struct edid *ge_b850v3_lvds_get_edid(struct drm_bridge *bridge,
>  
>  	client = ge_b850v3_lvds_ptr->stdp2690_i2c;
>  
> -	return (struct edid *)stdp2690_get_edid(client);
> +	return drm_do_get_edid(connector, stdp2690_read_block, client, NULL);

The last NULL param should be dropped, as noted by the build bot.

BR,
Jani.


>  }
>  
>  static int ge_b850v3_lvds_get_modes(struct drm_connector *connector)

-- 
Jani Nikula, Intel Open Source Graphics Center