Re: [PATCH v5 2/5] drm/msm/dsi: Adjust pclk rate for compression
From: Jessica Zhang
Date: Fri Jun 09 2023 - 13:24:41 EST
On 6/9/2023 9:58 AM, Dmitry Baryshkov wrote:
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@xxxxxxxxxxx>
---
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?
Hi Dmitry,
Correct, we will apply the compression ratio to only the hdisplay but
keep the porches as is.
[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.
Acked.
Thanks,
Jessica Zhang
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