Re: [PATCH] drm/omap: dsi: avoid sending bta sync all the time in writes

[Andreas Kemnade <andreas@kemnade.info>]

On Thu, 28 May 2026 22:06:03 +0200
Andreas Kemnade <andreas@kemnade.info> wrote:

> On Thu, 28 May 2026 20:43:12 +0300
> Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com> wrote:
> 
> > Hi,
> > 
> > On 28.05.26 г. 20:02 ч., Andreas Kemnade wrote:  
> > > Hi,
> > > 
> > > so this droid4? Or which device is it?
> > >     
> > 
> > Oh, sorry, yes, this is droid4.
> >   
> > > On Thu, 28 May 2026 17:44:14 +0300
> > > Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com> wrote:
> > >     
> > >> Applied against 6.18.31, no dice :)
> > >>
> > >> [   11.617523] [drm] Initialized pvr 1.17.4948957 for 56000000.gpu on
> > >> minor 0
> > >> [   11.674652] omapdss_dss 58000000.dss: bound 58001000.dispc (ops
> > >> dispc_component_ops [omapdrm])
> > >> [   11.775085] omapdss_dss 58000000.dss: bound 58001000.dispc (ops
> > >> dsi_vc_flush_receive_data [omapdrm])
> > >> [   12.222930] omapdss_dss 58000000.dss: bound 58001000.dispc (ops
> > >> dsi_vc_flush_receive_data [omapdrm])
> > >> [   12.245117] omapdss_dss 58000000.dss: bound 58001000.dispc (ops
> > >> dsi_vc_flush_receive_data [omapdrm])
> > >> [   12.247375] omapdss_dss 58000000.dss: bound 58004000.encoder (ops
> > >> dsi_vc_flush_receive_data [omapdrm])
> > >> [   12.249267] omapdss_dss 58000000.dss: bound 58006000.encoder (ops
> > >> dsi_vc_flush_receive_data [omapdrm])
> > >> [   12.284729] [drm] Initialized omapdrm 1.0.0 for omapdrm.0 on minor 1
> > >> [   12.311981] [drm] Enabling DMM ywrap scrolling    
> > > 
> > > I would expect some
> > > output from  the panel-dsi-cm driver:
> > > dev_info(&ddata->dsi->dev, "panel revision %02x.%02x.%02x\n",
> > >                          id1, id2, id3);
> > > 
> > > or some error:
> > >          dev_err(&ddata->dsi->dev, "error while enabling panel, issuing HW reset\n");
> > > 
> > > Any explanation why it is missing?
> > >     
> > 
> > It is there, I grep-ed for omapdrm only, didn't want to flood the ML:
> > 
> > 2026-05-28T17:34:45.761932+03:00 devuan-droid4 kernel: [   12.502105] 
> > panel-dsi-cm 58004000.encoder.0: panel revision 70.01.02
> > 
> > Here is the (almost)full boot log: https://paste.debian.net/hidden/e6ca55a7
> >   
> 2026-05-28T17:34:45.763732+03:00 devuan-droid4 kernel: [  112.820404] DSI: omapdss DSI: failed to send nop between frames: -5
> 2026-05-28T17:34:45.763732+03:00 devuan-droid4 kernel: [  113.331726] DSI: omapdss DSI: failed to send nop between frames: -5
> 
> and that is interesting. Apparently no PACKET_SENT_IRQ and the wait
> completion times out. Maybe it is not used with short packets.
> But..
>        /*
>          * Send NOP between the frames. If we don't send something here, the
>          * updates stop working. This is probably related to DSI spec stating
>          * that the DSI host should transition to LP at least once per frame.
>          */
>         r = _dsi_send_nop(dsi, VC_CMD, dsi->dsidev->channel);
> 
> I do not see a reason why something should go into LP mode here. the
> message will probably be sent in HS mode but the BTA sync (not done anymore)
> is probably the only thing turning something to LP mode.
> 
> So to avoid PACKET_SENT_IRQ trouble, do:
> diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
> index dcfcfc0efcdc..37323c9b08a8 100644
> --- a/drivers/gpu/drm/omapdrm/dss/dsi.c
> +++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
> @@ -2200,7 +2200,7 @@ static int dsi_vc_write_common(struct omap_dss_device *dssdev, int vc,
>  	int r;
>  
>  	if (mipi_dsi_packet_format_is_short(msg->type))
> -		r = dsi_vc_send_short(dsi, vc, msg);
> +		return dsi_vc_send_short(dsi, vc, msg);
>  	else
>  		r = dsi_vc_send_long(dsi, vc, msg);
>  
> 
> Also try:
> diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
> index dcfcfc0efcdc..37323c9b08a8 100644
> --- a/drivers/gpu/drm/omapdrm/dss/dsi.c
> +++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
> @@ -3283,11 +3283,11 @@ static int dsi_update_channel(struct omap_dss_device *dssdev, int vc)
>  	DSSDBG("dsi_update_channel: %d", vc);
>  
>  	/*
> -	 * Send NOP between the frames. If we don't send something here, the
> +	 * Transition to LP here. If we don't send something here, the
>  	 * updates stop working. This is probably related to DSI spec stating
>  	 * that the DSI host should transition to LP at least once per frame.
>  	 */
> -	r = _dsi_send_nop(dsi, VC_CMD, dsi->dsidev->channel);
> +	r = dsi_vc_send_bta_sync(dssdev, vc);

probably rather VC_CMD
>  	if (r < 0) {
>  		DSSWARN("failed to send nop between frames: %d\n", r);
>  		goto err;
> 
> 
> 
> Regards,
> Andreas
>