linux-kernel - Re: [PATCH v2] drm/bridge: Clear the DP_AUX_I2C

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Date:   Thu, 17 Feb 2022 16:31:19 +0800
From:   Xin Ji <xji@...logixsemi.com>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
Cc:     Robert Foss <robert.foss@...aro.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel@...ll.ch>,
        Andrzej Hajda <andrzej.hajda@...el.com>
Subject: Re: [PATCH v2] drm/bridge: Clear the DP_AUX_I2C_MOT bit passed in
 aux read command.

On Thu, Feb 17, 2022 at 04:22:25PM +0800, Hsin-Yi Wang wrote:
> If the previous transfer didn't end with a command without DP_AUX_I2C_MOT,
> the next read trasnfer will miss the first byte. But if the command in
> previous transfer is requested with length 0, it's a no-op to anx7625
> since it can't process this command. anx7625 requires the last command
> to be read command with length > 0.
> 
> It's observed that if we clear the DP_AUX_I2C_MOT in read transfer, we
> can still get correct data. Clear the read commands with DP_AUX_I2C_MOT
> bit to fix this issue.

Hi Hsin-Yi, thanks for the patch!

Reviewed-by: Xin Ji <xji@...logixsemi.com>

Thanks,
Xin
> 
> Fixes: adca62ec370c ("drm/bridge: anx7625: Support reading edid through aux channel")
> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> ---
> v1->v2: Offline discussed with Xin Ji, it's better to clear the bit on
> read commands only.
> ---
>  drivers/gpu/drm/bridge/analogix/anx7625.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c b/drivers/gpu/drm/bridge/analogix/anx7625.c
> index 633618bafd75d3..2805e9bed2c2f4 100644
> --- a/drivers/gpu/drm/bridge/analogix/anx7625.c
> +++ b/drivers/gpu/drm/bridge/analogix/anx7625.c
> @@ -253,6 +253,8 @@ static int anx7625_aux_trans(struct anx7625_data *ctx, u8 op, u32 address,
>  	addrm = (address >> 8) & 0xFF;
>  	addrh = (address >> 16) & 0xFF;
>  
> +	if (!is_write)
> +		op &= ~DP_AUX_I2C_MOT;
>  	cmd = DPCD_CMD(len, op);
>  
>  	/* Set command and length */
> -- 
> 2.35.1.265.g69c8d7142f-goog