Re: [PATCH v3 7/7] drm/bridge: ti-sn65dsi86: Add mystery delay to enable()

[spanda@codeaurora.org]

On 2018-08-14 03:00, Sean Paul wrote:
> From: Sean Paul <seanpaul@chromium.org>
> 
> This patch adds a 70ms mystery delay to the bridge driver in enable.
> By experimentation, it seems like it can go anywhere up until we
> initiate semi-auto link training. If we don't have the delay, link
> training fails.
> 
> I tried to root cause this as best I could, but neither the datasheet
> for the panel nor the bridge mention a delay of this magnitude in their
> timing requirements. So for now, add the mystery delay until someone
> figures out a better fix.
> 
> Changes in v3:
> - Added to the set
> 
> Cc: Sandeep Panda <spanda@codeaurora.org>
> Signed-off-by: Sean Paul <seanpaul@chromium.org>
> ---
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index d3e27e52ea759..f8a931cf3665e 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -458,6 +458,18 @@ static void ti_sn_bridge_enable(struct drm_bridge 
> *bridge)
>  	unsigned int val;
>  	int ret;
> 
> +	/*
> +	 * FIXME:
> +	 * This 70ms was found necessary by experimentation. If it's not
> +	 * present, link training fails. It seems like it can go anywhere 
> from
> +	 * pre_enable() up to semi-auto link training initiation below.
> +	 *
> +	 * Neither the datasheet for the bridge nor the panel tested mention 
> a
> +	 * delay of this magnitude in the timing requirements. So for now, 
> add
> +	 * the mystery delay until someone figures out a better fix.
> +	 */

Is this newly found issue? Specific to any board config?

> +	msleep(70);
> +
>  	/* DSI_A lane config */
>  	val = CHA_DSI_LANES(4 - pdata->dsi->lanes);
>  	regmap_update_bits(pdata->regmap, SN_DSI_LANES_REG,
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