Re: [PATCH v2 4/6] drm/msm/dsi: add a comment to explain pkt_per_line encoding

[Dmitry Baryshkov]

On 16/11/2023 20:45, Jonathan Marek wrote:
> On 11/15/23 2:38 AM, Dmitry Baryshkov wrote:
> > On Wed, 15 Nov 2023 at 01:00, Jonathan Marek <jonathan@xxxxxxxx> wrote:
> > > Make it clear why the pkt_per_line value is being "divided by 2".
> > >
> > > Signed-off-by: Jonathan Marek <jonathan@xxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/msm/dsi/dsi_host.c | 2 ++
> > >   1 file changed, 2 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c 
> > > b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > > index 66f198e21a7e..842765063b1b 100644
> > > --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> > > +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > > @@ -877,6 +877,8 @@ static void dsi_update_dsc_timing(struct 
> > > msm_dsi_host *msm_host, bool is_cmd_mod
> > >          /* DSI_VIDEO_COMPRESSION_MODE & DSI_COMMAND_COMPRESSION_MODE
> > >           * registers have similar offsets, so for below common code use
> > >           * DSI_VIDEO_COMPRESSION_MODE_XXXX for setting bits
> > > +        *
> > > +        * pkt_per_line is log2 encoded, >>1 works for supported 
> > > values (1,2,4)
> > >           */
> > >          reg |= 
> > > DSI_VIDEO_COMPRESSION_MODE_CTRL_PKT_PER_LINE(pkt_per_line >> 1);
> >
> > Should we switch to ffs() or fls() instead?
>
> Just a ffs() on its own can be confusing as well (without the 
> information that only powers of two are possible), I think like this is 
> better.

Sounds fair. Could you please then add `if (pkt_per_line > 4) 
drm_warn("pkt_per_line too big");`

With that in place:

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>

> > >          reg |= 
> > > DSI_VIDEO_COMPRESSION_MODE_CTRL_EOL_BYTE_NUM(eol_byte_num);
> > > --
> > > 2.26.1

--
With best wishes
Dmitry