Re: [Intel-gfx] [PATCH] drm/i915/dsi: Use unconditional msleep for the panel_on_delay when there is no reset-deassert MIPI-sequence

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Nov 18, 2020 at 01:40:58PM +0100, Hans de Goede wrote:
> Commit 25b4620ee822 ("drm/i915/dsi: Skip delays for v3 VBTs in vid-mode")
> added an intel_dsi_msleep() helper which skips sleeping if the
> MIPI-sequences have a version of 3 or newer and the panel is in vid-mode;
> and it moved a bunch of msleep-s over to this new helper.
> 
> This was based on my reading of the big comment around line 730 which
> starts with "Panel enable/disable sequences from the VBT spec.",
> where the "v3 video mode seq" column does not have any wait t# entries.
> 
> Given that this code has been used on a lot of different devices without
> issues until now, it seems that my interpretation of the spec here is
> mostly correct.
> 
> But now I have encountered one device, an Acer Aspire Switch 10 E
> SW3-016, where the panel will not light up unless we do actually honor the
> panel_on_delay after exexuting the MIPI_SEQ_PANEL_ON sequence.
> 
> What seems to set this model apart is that it is lacking a
> MIPI_SEQ_DEASSERT_RESET sequence, which is where the power-on
> delay usually happens.
> 
> Fix the panel not lighting up on this model by using an unconditional
> msleep(panel_on_delay) instead of intel_dsi_msleep() when there is
> no MIPI_SEQ_DEASSERT_RESET sequence.
> 
> Fixes: 25b4620ee822 ("drm/i915/dsi: Skip delays for v3 VBTs in vid-mode")
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  drivers/gpu/drm/i915/display/vlv_dsi.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/vlv_dsi.c b/drivers/gpu/drm/i915/display/vlv_dsi.c
> index 194c239ab6b1..ef673277b36d 100644
> --- a/drivers/gpu/drm/i915/display/vlv_dsi.c
> +++ b/drivers/gpu/drm/i915/display/vlv_dsi.c
> @@ -816,10 +816,14 @@ static void intel_dsi_pre_enable(struct intel_atomic_state *state,
>  		intel_dsi_prepare(encoder, pipe_config);
>  
>  	intel_dsi_vbt_exec_sequence(intel_dsi, MIPI_SEQ_POWER_ON);
> -	intel_dsi_msleep(intel_dsi, intel_dsi->panel_on_delay);
>  
> -	/* Deassert reset */
> -	intel_dsi_vbt_exec_sequence(intel_dsi, MIPI_SEQ_DEASSERT_RESET);
> +	if (dev_priv->vbt.dsi.sequence[MIPI_SEQ_DEASSERT_RESET]) {
> +		intel_dsi_msleep(intel_dsi, intel_dsi->panel_on_delay);
> +		/* Deassert reset */
> +		intel_dsi_vbt_exec_sequence(intel_dsi, MIPI_SEQ_DEASSERT_RESET);
> +	} else {
> +		msleep(intel_dsi->panel_on_delay);
> +	}

Could perhaps use a comment ot explain to the reader what's going on.

Looks sane enough to me, and if we get this wrong we just get a bigger
delay than necessary I guess. So mostly harmless.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  
>  	if (IS_GEMINILAKE(dev_priv)) {
>  		glk_cold_boot = glk_dsi_enable_io(encoder);
> -- 
> 2.28.0

-- 
Ville Syrjälä
Intel
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