On Fri, Oct 11, 2019 at 06:39:39AM -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@xxxxxxxxx>
Pushed to drm-misc-fixes for 5.4
Thanks!
Sean
> Reviewed-by: Sean Paul <sean@xxxxxxxxxx>
> ---
>
> v2:
> -make a DEFINE for the delay
>
> drivers/gpu/drm/msm/dsi/dsi_host.c | 6 ++++--
> 1 file changed, 4 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..9a81705301c6 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -26,6 +26,8 @@
> #include "dsi_cfg.h"
> #include "msm_kms.h"
>
> +#define RESET_DELAY 20
> +
> static int dsi_get_version(const void __iomem *base, u32 *major, u32 *minor)
> {
> u32 ver;
> @@ -986,7 +988,7 @@ 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(RESET_DELAY); /* make sure reset happen */
> dsi_write(msm_host, REG_DSI_RESET, 0);
> }
>
> @@ -1396,7 +1398,7 @@ 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(RESET_DELAY); /* 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
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