Re: [PATCH] drm/msm/dsi: Enable BURST_MODE for command mode for DSI 6G v1.3+

[Jessica Zhang]

On 6/14/2023 2:43 AM, Marijn Suijten wrote:
> On 2023-06-12 16:37:36, Jessica Zhang wrote:
> > During a frame transfer in command mode, there could be frequent
> > LP11 <-> HS transitions when multiple DCS commands are sent mid-frame or
> > if the DSI controller is running on slow clock and is throttled. To
> > minimize frame latency due to these transitions, it is recommended to
> > send the frame in a single burst.
> >
> > This feature is supported for DSI 6G 1.3 and above, thus enable burst
> > mode if supported.
> >
> > Signed-off-by: Jessica Zhang <quic_jesszhan@xxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/msm/dsi/dsi_host.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > index 744f2398a6d6..8254b06dca85 100644
> > --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> > +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > @@ -994,6 +994,11 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
> >   		dsi_write(msm_host, REG_DSI_CMD_MDP_STREAM0_TOTAL,
> >   			DSI_CMD_MDP_STREAM0_TOTAL_H_TOTAL(hdisplay) |
> >   			DSI_CMD_MDP_STREAM0_TOTAL_V_TOTAL(mode->vdisplay));
> > +
> > +		if (msm_host->cfg_hnd->major == MSM_DSI_VER_MAJOR_6G &&
> > +				msm_host->cfg_hnd->minor >= MSM_DSI_6G_VER_MINOR_V1_3)
> > +			dsi_write(msm_host, REG_DSI_CMD_MODE_MDP_CTRL2,
> > +					DSI_CMD_MODE_MDP_CTRL2_BURST_MODE);
>
> This is not part of the timing setup, and a similar BURST_MODE flag is
> enabled for video-mode in dsi_ctrl_config() - should it be moved there?

Hi Marijn,

Sure, I can move the change to dsi_ctrl_enable() instead.

> (There is a dsi_sw_reset() in between the calls to dsi_timing_setup()
>   and dsi_ctrl_cfg())
>
> Note that that function sets up the CMD_CFG0 and CMD_CFG1 register, with
> the former having a very similar layout to MDP_CTRL2... is there
> documentation outlining the difference?

I see what you mean, but unfortunately I'm not able to give you any 
documentation about the differences between them.

FWIW, I think the macros in dsi.xml.h should give you a sense of what's 
within the registers and the slight differences between them.

Thanks,

Jessica Zhang

> - Marijn
>
> >   	}
> >   }
> >   
> >
> > ---
> > base-commit: dd969f852ba4c66938c71889e826aa8e5300d2f2
> > change-id: 20230608-b4-add-burst-mode-a5bb144069fa
> >
> > Best regards,
> > --
> > Jessica Zhang <quic_jesszhan@xxxxxxxxxxx>