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Message-ID: <5b75dckankcx55gbm734a23rvqxdbprlus3nkvqfry7lz5ksjf@jjmfsbiwqny6>
Date: Wed, 24 Sep 2025 22:10:52 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Jun Nie <jun.nie@...aro.org>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
Abhinav Kumar <abhinav.kumar@...ux.dev>,
Jessica Zhang <jessica.zhang@....qualcomm.com>,
Dmitry Baryshkov <lumag@...nel.org>, Sean Paul <sean@...rly.run>,
Marijn Suijten <marijn.suijten@...ainline.org>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>,
Krishna Manikandan <quic_mkrishn@...cinc.com>,
linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
devicetree@...r.kernel.org, Jonathan Marek <jonathan@...ek.ca>
Subject: Re: [PATCH v3 1/3] drm/msm/dsi: support DSC configurations with
slice_per_pkt > 1
On Wed, Sep 24, 2025 at 11:08:10PM +0800, Jun Nie wrote:
> Some panels support multiple slice to be sent in a single DSC packet. And
s/support/require/
If the panel supports something, then we can omit that and send 1 slice
as we currently do. If the panel requires multiple slices, it's
mandatory.
> this feature is a must for specific panels, such as JDI LPM026M648C. Add a
A panel driver which executes this API is appreciated. Otherwise in a
few months / years somebody will submit a patch 'field foo is not used
by the kernel drivers, drop it'.
> dsc_slice_per_pkt member into struct mipi_dsi_device and support the
> feature in msm mdss driver.
>
> Co-developed-by: Jonathan Marek <jonathan@...ek.ca>
> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
> Signed-off-by: Jun Nie <jun.nie@...aro.org>
> ---
> drivers/gpu/drm/msm/dsi/dsi_host.c | 25 ++++++++++---------------
> include/drm/drm_mipi_dsi.h | 2 ++
> 2 files changed, 12 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index f297e3de8c3dc4e1326e70c78c046b5a19568cef..de51cb02f267205320c5a94fc4188413e05907e6 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -157,6 +157,7 @@ struct msm_dsi_host {
>
> struct drm_display_mode *mode;
> struct drm_dsc_config *dsc;
> + unsigned int dsc_slice_per_pkt;
>
> /* connected device info */
> unsigned int channel;
> @@ -849,17 +850,10 @@ static void dsi_update_dsc_timing(struct msm_dsi_host *msm_host, bool is_cmd_mod
> slice_per_intf = dsc->slice_count;
>
> total_bytes_per_intf = dsc->slice_chunk_size * slice_per_intf;
> - bytes_per_pkt = dsc->slice_chunk_size; /* * slice_per_pkt; */
> + bytes_per_pkt = dsc->slice_chunk_size * msm_host->dsc_slice_per_pkt;
>
> eol_byte_num = total_bytes_per_intf % 3;
> -
> - /*
> - * 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;
> + pkt_per_line = slice_per_intf / msm_host->dsc_slice_per_pkt;
>
> if (is_cmd_mode) /* packet data type */
> reg = DSI_COMMAND_COMPRESSION_MODE_CTRL_STREAM0_DATATYPE(MIPI_DSI_DCS_LONG_WRITE);
> @@ -1008,12 +1002,8 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
> else
> /*
> * When DSC is enabled, WC = slice_chunk_size * slice_per_pkt + 1.
> - * Currently, the driver only supports default value of slice_per_pkt = 1
> - *
> - * TODO: Expand mipi_dsi_device struct to hold slice_per_pkt info
> - * and adjust DSC math to account for slice_per_pkt.
> */
> - wc = msm_host->dsc->slice_chunk_size + 1;
> + wc = msm_host->dsc->slice_chunk_size * msm_host->dsc_slice_per_pkt + 1;
>
> dsi_write(msm_host, REG_DSI_CMD_MDP_STREAM0_CTRL,
> DSI_CMD_MDP_STREAM0_CTRL_WORD_COUNT(wc) |
> @@ -1623,8 +1613,13 @@ static int dsi_host_attach(struct mipi_dsi_host *host,
> msm_host->lanes = dsi->lanes;
> msm_host->format = dsi->format;
> msm_host->mode_flags = dsi->mode_flags;
> - if (dsi->dsc)
> + if (dsi->dsc) {
> msm_host->dsc = dsi->dsc;
> + msm_host->dsc_slice_per_pkt = dsi->dsc_slice_per_pkt;
> + /* for backwards compatibility, assume 1 if not set */
> + if (!msm_host->dsc_slice_per_pkt)
> + msm_host->dsc_slice_per_pkt = 1;
msm_host->dsc_slice_per_pkt = dsi->dsc_slice_per_pkt ?: 1;
Yes, I think it's more ideomatic.
> + }
>
> ret = dsi_dev_attach(msm_host->pdev);
> if (ret)
> diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
> index 6d2c08e8110151a97620389197f1ef79c058329d..5a85ba01f402a3866b70828391bb417bb8dd5956 100644
> --- a/include/drm/drm_mipi_dsi.h
> +++ b/include/drm/drm_mipi_dsi.h
> @@ -182,6 +182,7 @@ struct mipi_dsi_device_info {
> * be set to the real limits of the hardware, zero is only accepted for
> * legacy drivers
> * @dsc: panel/bridge DSC pps payload to be sent
> + * @dsc_slice_per_pkt: number of DSC slices to be sent as in a single packet
s/as //
> */
> struct mipi_dsi_device {
> struct mipi_dsi_host *host;
> @@ -196,6 +197,7 @@ struct mipi_dsi_device {
> unsigned long hs_rate;
> unsigned long lp_rate;
> struct drm_dsc_config *dsc;
> + unsigned int dsc_slice_per_pkt;
Why is it a part of the DSI device config? What if a device specifies
dsc_slice_per_pkt, but not DSC config? What are the legit boundaries for
this field?
> };
>
> /**
>
> --
> 2.34.1
>
--
With best wishes
Dmitry
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