lkml.org 
[lkml]   [2019]   [Oct]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] drm/msm/dsi: Implement reset correctly
On Wed, Oct 09, 2019 at 02:34:54PM -0700, Jeffrey Hugo wrote:
> On msm8998, vblank timeouts are observed because the DSI controller is not
> reset properly, which ends up stalling the MDP. This is because the reset
> logic is not correct per the hardware documentation.
>
> The documentation states that after asserting reset, software should wait
> some time (no indication of how long), or poll the status register until it
> returns 0 before deasserting reset.
>
> wmb() is insufficient for this purpose since it just ensures ordering, not
> timing between writes. Since asserting and deasserting reset occurs on the
> same register, ordering is already guaranteed by the architecture, making
> the wmb extraneous.
>
> Since we would define a timeout for polling the status register to avoid a
> possible infinite loop, lets just use a static delay of 20 ms, since 16.666
> ms is the time available to process one frame at 60 fps.
>
> Fixes: a689554ba6ed (drm/msm: Initial add DSI connector support)
> Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
> ---
>
> Rob et al, is it possible for this to go into a 5.4-rc?
>
> drivers/gpu/drm/msm/dsi/dsi_host.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 663ff9f4fac9..68ded9b4735d 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -986,7 +986,7 @@ static void dsi_sw_reset(struct msm_dsi_host *msm_host)
> wmb(); /* clocks need to be enabled before reset */
>
> dsi_write(msm_host, REG_DSI_RESET, 1);
> - wmb(); /* make sure reset happen */
> + msleep(20); /* make sure reset happen */

Could you please pull this out into a #define used for both in case we decide to
tweak it? I don't want these 2 values to drift.

Thanks,
Sean

> dsi_write(msm_host, REG_DSI_RESET, 0);
> }
>
> @@ -1396,7 +1396,7 @@ static void dsi_sw_reset_restore(struct msm_dsi_host *msm_host)
>
> /* dsi controller can only be reset while clocks are running */
> dsi_write(msm_host, REG_DSI_RESET, 1);
> - wmb(); /* make sure reset happen */
> + msleep(20); /* make sure reset happen */
> dsi_write(msm_host, REG_DSI_RESET, 0);
> wmb(); /* controller out of reset */
> dsi_write(msm_host, REG_DSI_CTRL, data0);
> --
> 2.17.1
>

--
Sean Paul, Software Engineer, Google / Chromium OS

\
 
 \ /
  Last update: 2019-10-10 20:46    [W:0.288 / U:0.080 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site