Messages in this thread | | | Date | Fri, 9 Jun 2023 19:58:00 +0300 | Subject | Re: [PATCH v5 2/5] drm/msm/dsi: Adjust pclk rate for compression | From | Dmitry Baryshkov <> |
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On 08/06/2023 23:36, Marijn Suijten wrote: > Same title suggestion as earlier: s/adjust/reduce > > On 2023-05-22 18:08:56, Jessica Zhang wrote: >> Adjust the pclk rate to divide hdisplay by the compression ratio when DSC >> is enabled. >> >> Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com> >> --- >> drivers/gpu/drm/msm/dsi/dsi_host.c | 21 ++++++++++++++++++--- >> 1 file changed, 18 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c >> index a448931af804..88f370dd2ea1 100644 >> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c >> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c >> @@ -561,7 +561,18 @@ void dsi_link_clk_disable_v2(struct msm_dsi_host *msm_host) >> clk_disable_unprepare(msm_host->byte_clk); >> } >> >> -static unsigned long dsi_get_pclk_rate(const struct drm_display_mode *mode, bool is_bonded_dsi) >> +static unsigned long dsi_adjust_compressed_pclk(const struct drm_display_mode *mode, > > Nit: adjust_pclk_for_compression > > As discussed before we realized that this change is more-or-less a hack, > since downstream calculates pclk quite differently - at least for > command-mode panels. Do you still intend to land this patch this way, > or go the proper route by introducing the right math from the get-go? > Or is the math at least correct for video-mode panels?
Can we please postpone the cmd-vs-video discussion? Otherwise I will reserve myself a right to push a patch dropping CMD mode support until somebody comes with a proper way to handle CMD clock calculation.
It is off-topic for the sake of DSC 1.2 support. Yes, all CMD panel timings are a kind of a hack and should be improved. No, we can not do this as a part of this series. I think everybody agrees that with the current way of calculating CMD panel timings, this function does some kind of a trick.
> > This function requires a documentation comment to explain that all. > >> + const struct drm_dsc_config *dsc) >> +{ >> + int new_hdisplay = DIV_ROUND_UP(mode->hdisplay * drm_dsc_get_bpp_int(dsc), > > This sounds like a prime candidate for msm_dsc_get_bytes_per_line(), if > bits_per_component==8 is assumed. In fact, it then becomes identical > to the following line in dsi_host.c which you added previously: > > hdisplay = DIV_ROUND_UP(msm_dsc_get_bytes_per_line(msm_host->dsc), 3);
This would imply a simple /3, but as far as I understand it is not correct here.
> > If not, what is the difference between these two calculations? Maybe > they both need to be in a properly-named helper. > >> + dsc->bits_per_component * 3);
I hope to see a documentation patch to be posted, telling that this scales hdisplay and thus pclk by the factor of compressed_bpp / uncompressed_bpp.
This is not how it is usually done, but I would accept a separate documentation patch going over the calculation here and in dsi_timing_setup (and maybe other unobvious cases, if there is anything left).
> > As we established in the drm/msm issue [2] there is currently a > confusion whether this /3 (and the /3 in dsi_timing_setup) come from the > ratio between dsi_get_bpp() and dsc->bpp or something else. Can you > clarify that with constants and comments? > > [2]: https://gitlab.freedesktop.org/drm/msm/-/issues/24 > >> + >> + return (new_hdisplay + (mode->htotal - mode->hdisplay)) >> + * mode->vtotal * drm_mode_vrefresh(mode); > > As clarified in [1] I was not necessarily suggesting to move this math > to a separate helper, but to also use a few more properly-named > intermediate variables to not have multi-line math and self-documenting > code. These lines could be split to be much more clear.
I think it's fine more or less. One pair of parenthesis is unnecessary, but that's mostly it. Maybe `new_htotal' variable would make some sense.
Also, please excuse me if this was discussed somewhere. This calculation means that only the displayed data is compressed, but porches are not touched. Correct?
> > [1]: https://lore.kernel.org/linux-arm-msm/u4x2vldkzsokfcpbkz3dtwcllbdk4ljcz6kzuaxt5frx6g76o5@uku6abewvye7/ > >> +} >> + >> +static unsigned long dsi_get_pclk_rate(const struct drm_display_mode *mode, >> + const struct drm_dsc_config *dsc, bool is_bonded_dsi) >> { >> unsigned long pclk_rate; >> >> @@ -576,6 +587,10 @@ static unsigned long dsi_get_pclk_rate(const struct drm_display_mode *mode, bool >> if (is_bonded_dsi) >> pclk_rate /= 2; >> >> + /* If DSC is enabled, divide hdisplay by compression ratio */ >> + if (dsc) >> + pclk_rate = dsi_adjust_compressed_pclk(mode, dsc);
Looking for the perfection, I'd also move the pclk adjustment to come before the is_bonded_dsi check.
> > The confusion with this comment (and the reason the aforementioned > discussion [2] carried on so long) stems from the fact a division makes > sense for a bit/byte clock, but not for a pixel clock: we still intend > to send the same number of pixels, just spending less bytes on them. So > as you clarify the /3 above, can you also clarify that here or drop this > comment completely when the function is correctly documented instead? > > - Marijn > >> + >> return pclk_rate; >> } >> >> @@ -585,7 +600,7 @@ unsigned long dsi_byte_clk_get_rate(struct mipi_dsi_host *host, bool is_bonded_d >> struct msm_dsi_host *msm_host = to_msm_dsi_host(host); >> u8 lanes = msm_host->lanes; >> u32 bpp = dsi_get_bpp(msm_host->format); >> - unsigned long pclk_rate = dsi_get_pclk_rate(mode, is_bonded_dsi); >> + unsigned long pclk_rate = dsi_get_pclk_rate(mode, msm_host->dsc, is_bonded_dsi); >> unsigned long pclk_bpp; >> >> if (lanes == 0) { >> @@ -604,7 +619,7 @@ unsigned long dsi_byte_clk_get_rate(struct mipi_dsi_host *host, bool is_bonded_d >> >> static void dsi_calc_pclk(struct msm_dsi_host *msm_host, bool is_bonded_dsi) >> { >> - msm_host->pixel_clk_rate = dsi_get_pclk_rate(msm_host->mode, is_bonded_dsi); >> + msm_host->pixel_clk_rate = dsi_get_pclk_rate(msm_host->mode, msm_host->dsc, is_bonded_dsi); >> msm_host->byte_clk_rate = dsi_byte_clk_get_rate(&msm_host->base, is_bonded_dsi, >> msm_host->mode); >> >> >> -- >> 2.40.1 >>
-- With best wishes Dmitry
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