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

[Jani Nikula]

On Fri, 08 Sep 2023, Ian Ray <ian.ray at ge.com> wrote:
> On Fri, Sep 01, 2023 at 05:52:02PM +0300, Jani Nikula wrote:
>> 
>> On Fri, 01 Sep 2023, Jani Nikula <jani.nikula at 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 at intel.com>
>> > Cc: Ian Ray <ian.ray at ge.com>
>> > Cc: Jernej Skrabec <jernej.skrabec at gmail.com>
>> > Cc: Jonas Karlman <jonas at kwiboo.se>
>> > Cc: Laurent Pinchart <Laurent.pinchart at ideasonboard.com>
>> > Cc: Martin Donnelly <martin.donnelly at ge.com>
>> > Cc: Martyn Welch <martyn.welch at collabora.co.uk>
>> > Cc: Neil Armstrong <neil.armstrong at linaro.org>
>> > Cc: Peter Senna Tschudin <peter.senna at gmail.com>
>> > Cc: Robert Foss <rfoss at kernel.org>
>> > Cc: Yuan Can <yuancan at huawei.com>
>> > Cc: Zheyu Ma <zheyuma97 at gmail.com>
>> > Signed-off-by: Jani Nikula <jani.nikula at 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.
>
> Tested with various displays, including displays that have one block of
> EDID (DELL P2417H) and a second EDID extension block (VES/55UHD_LCD_TV).
>
> Tested-by: Ian Ray <ian.ray at ge.com>
>
> Would you like me to submit the patch Jani?

If you have the time to take that on, by all means!

Thanks for testing!

BR,
Jani


>
>
>> 
>> BR,
>> Jani.
>> 
>> 
>> >  }
>> >  
>> >  static int ge_b850v3_lvds_get_modes(struct drm_connector *connector)
>> 
>> -- 
>> Jani Nikula, Intel Open Source Graphics Center
>> 

-- 
Jani Nikula, Intel