Re: [PATCH v4 5/5] drm/msm/dsi: Remove incorrect references to slice_count

[Jessica Zhang]

On 5/22/2023 2:01 PM, Marijn Suijten wrote:
> On 2023-05-22 13:30:24, Jessica Zhang wrote:
> > Currently, slice_count is being used to calculate word count and
> > pkt_per_line. Instead, these values should be calculated using slice per
> > packet, which is not the same as slice_count.
> >
> > Slice count represents the number of soft slices per interface, and its
> > value will not always match that of slice per packet. For example, it is
> > possible to have cases where there are multiple soft slices per interface
> > but the panel specifies only one slice per packet.
>
> As discussed in many patches before, there is no definition of "soft
> slices" anyhwere.  Unless we can have that, and reference it, this
> should more clearly explain what it means or leave out the word "soft"
> altogether.

Hi Marijn,

Acked.

> > Thus, use the default value of one slice per packet and remove slice_count
> > from the aforementioned calculations.
> >
> > Fixes: 08802f515c3c ("drm/msm/dsi: Add support for DSC configuration")
> > Fixes: bc6b6ff8135c ("drm/msm/dsi: Use DSC slice(s) packet size to compute word count")
> > Signed-off-by: Jessica Zhang <quic_jesszhan@xxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/msm/dsi/dsi_host.c | 26 ++++++++++++++++----------
> >   1 file changed, 16 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > index d04f8bbd707d..2eed99afdba9 100644
> > --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> > +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > @@ -866,18 +866,17 @@ static void dsi_update_dsc_timing(struct msm_dsi_host *msm_host, bool is_cmd_mod
> >   	 */
> >   	slice_per_intf = msm_dsc_get_slices_per_intf(dsc, hdisplay);
> >   
> > -	/*
> > -	 * If slice_count is greater than slice_per_intf
> > -	 * then default to 1. This can happen during partial
> > -	 * update.
> > -	 */
> > -	if (dsc->slice_count > slice_per_intf)
> > -		dsc->slice_count = 1;
> > -
> >   	total_bytes_per_intf = dsc->slice_chunk_size * slice_per_intf;
> >   
> >   	eol_byte_num = total_bytes_per_intf % 3;
> > -	pkt_per_line = slice_per_intf / dsc->slice_count;
> > +
> > +	/*
> > +	 * Typically, pkt_per_line = slice_per_intf * slice_per_pkt.
> > +	 *
> > +	 * Since the current driver only supports slice_per_pkt = 1,
> > +	 * pkt_per_line will be equal to slice per intf for now.
> > +	 */
> > +	pkt_per_line = slice_per_intf;
> >   
> >   	if (is_cmd_mode) /* packet data type */
> >   		reg = DSI_COMMAND_COMPRESSION_MODE_CTRL_STREAM0_DATATYPE(MIPI_DSI_DCS_LONG_WRITE);
> > @@ -1001,7 +1000,14 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
> >   		if (!msm_host->dsc)
> >   			wc = hdisplay * dsi_get_bpp(msm_host->format) / 8 + 1;
> >   		else
> > -			wc = msm_host->dsc->slice_chunk_size * msm_host->dsc->slice_count + 1;
> > +			/*
> > +			 * When DSC is enabled, WC = slice_chunk_size * slice_per_packet + 1.
> > +			 * Currently, the driver only supports default value of slice_per_packet = 1
> > +			 *
> > +			 * TODO: Expand mipi_dsi_device struct to hold slice_per_packet info
> > +			 *       and adjust DSC math to account for slice_per_packet.
> > +			 */
>
> Either rename this all to slice_per_pkt, or rename the above comment to
> slice_per_packet.

Acked.

Thanks,

Jessica Zhang

> After improving on that:
>
> Reviewed-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
>
> We all learned the wrong thing initially, thanks for clearing up that
> slice_count != slice_per_pkt.
>
> - Marijn
>
> > +			wc = msm_host->dsc->slice_chunk_size + 1;
> >   
> >   		dsi_write(msm_host, REG_DSI_CMD_MDP_STREAM0_CTRL,
> >   			DSI_CMD_MDP_STREAM0_CTRL_WORD_COUNT(wc) |
> >
> > --
> > 2.40.1