Message-ID: <20211211000315.pavmcc7cc73ilb6l@SoMainline.org>
Date:   Sat, 11 Dec 2021 01:03:15 +0100
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Rob Clark <robdclark@...il.com>, linux-arm-msm@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Marek <jonathan@...ek.ca>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org,
        Konrad Dybcio <konrad.dybcio@...ainline.org>
Subject: Re: [PATCH v3 12/13] drm/msm/dsi: Add support for DSC configuration

Hi Vinod,

On 2021-11-16 11:52:55, Vinod Koul wrote:
> When DSC is enabled, we need to configure DSI registers accordingly and
> configure the respective stream compression registers.
> 
> Add support to calculate the register setting based on DSC params and
> timing information and configure these registers.
> 
> Signed-off-by: Vinod Koul <vkoul@...nel.org>
> ---
>  drivers/gpu/drm/msm/dsi/dsi.xml.h  |  10 +++
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 113 ++++++++++++++++++++++++++++-
>  2 files changed, 122 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi.xml.h b/drivers/gpu/drm/msm/dsi/dsi.xml.h
> index 49b551ad1bff..c1c85df58c4b 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi.xml.h
> +++ b/drivers/gpu/drm/msm/dsi/dsi.xml.h
> @@ -706,4 +706,14 @@ static inline uint32_t DSI_VERSION_MAJOR(uint32_t val)
>  #define REG_DSI_CPHY_MODE_CTRL					0x000002d4
>  
>  
> +#define REG_DSI_VIDEO_COMPRESSION_MODE_CTRL			0x0000029c
> +
> +#define REG_DSI_VIDEO_COMPRESSION_MODE_CTRL2			0x000002a0
> +
> +#define REG_DSI_COMMAND_COMPRESSION_MODE_CTRL			0x000002a4
> +
> +#define REG_DSI_COMMAND_COMPRESSION_MODE_CTRL2			0x000002a8
> +
> +#define REG_DSI_COMMAND_COMPRESSION_MODE_CTRL3			0x000002ac

I presume you are aware that these files are autogenerated, but there
does not seem to be any link to patches adding these registers to the
XML files in either envytools to mesa, nor could I find any merge/pull
requests on the matter.  Would you mind posting those?  Before doing so
though, consider the comment below about register mapping.

> +
>  #endif /* DSI_XML */
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 31d385d8d834..2c14c36f0b3d 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -908,6 +908,20 @@ static void dsi_ctrl_config(struct msm_dsi_host *msm_host, bool enable,
>  		dsi_write(msm_host, REG_DSI_CPHY_MODE_CTRL, BIT(0));
>  }
>  
> +static int dsi_dsc_update_pic_dim(struct msm_display_dsc_config *dsc,
> +				  int pic_width, int pic_height)

This function - adopted from downstream - does not seem to perform a
whole lot, especially without the modulo checks against the slice size.
Perhaps it can be inlined?

> +{
> +	if (!dsc || !pic_width || !pic_height) {
> +		pr_err("DSI: invalid input: pic_width: %d pic_height: %d\n", pic_width, pic_height);
> +		return -EINVAL;
> +	}
> +
> +	dsc->drm->pic_width = pic_width;
> +	dsc->drm->pic_height = pic_height;
> +
> +	return 0;
> +}
> +
>  static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
>  {
>  	struct drm_display_mode *mode = msm_host->mode;
> @@ -940,7 +954,68 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
>  		hdisplay /= 2;
>  	}
>  
> +	if (msm_host->dsc) {
> +		struct msm_display_dsc_config *dsc = msm_host->dsc;
> +
> +		/* update dsc params with timing params */
> +		dsi_dsc_update_pic_dim(dsc, mode->hdisplay, mode->vdisplay);
> +		DBG("Mode Width- %d x Height %d\n", dsc->drm->pic_width, dsc->drm->pic_height);

This seems to be pretty non-standard and perhaps unnecessary debug code,
with a stray dash in there.  Is is needed here, and if so how about
using %dx%d\n to format width and height?

> +
> +		/* we do the calculations for dsc parameters here so that
> +		 * panel can use these parameters
> +		 */
> +		dsi_populate_dsc_params(dsc);
> +
> +		/* Divide the display by 3 but keep back/font porch and
> +		 * pulse width same
> +		 */

A more general nit on the comments in this patch series: it is
appreciated if comments explain the rationale rather than - or in
addition to - merely paraphrasing the code that follows.

> +		h_total -= hdisplay;
> +		hdisplay /= 3;
> +		h_total += hdisplay;
> +		ha_end = ha_start + hdisplay;
> +	}
> +
>  	if (msm_host->mode_flags & MIPI_DSI_MODE_VIDEO) {
> +		if (msm_host->dsc) {
> +			struct msm_display_dsc_config *dsc = msm_host->dsc;
> +			u32 reg, intf_width, slice_per_intf;
> +			u32 total_bytes_per_intf;
> +
> +			/* first calculate dsc parameters and then program
> +			 * compress mode registers
> +			 */
> +			intf_width = hdisplay;
> +			slice_per_intf = DIV_ROUND_UP(intf_width, dsc->drm->slice_width);
> +
> +			dsc->drm->slice_count = 1;
> +			dsc->bytes_in_slice = DIV_ROUND_UP(dsc->drm->slice_width * 8, 8);

If I am not mistaken this is the same value as dsc->drm->slice_width,
since a multiple of 8 is inherently "a multiple of 8" and hence needs no
rounding when divided by 8 again.

Also note that the cmdmode variant below uses bits_per_pixel here; is
that discrepancy intended?

> +			total_bytes_per_intf = dsc->bytes_in_slice * slice_per_intf;
> +
> +			dsc->eol_byte_num = total_bytes_per_intf % 3;
> +			dsc->pclk_per_line =  DIV_ROUND_UP(total_bytes_per_intf, 3);
> +			dsc->bytes_per_pkt = dsc->bytes_in_slice * dsc->drm->slice_count;
> +			dsc->pkt_per_line = slice_per_intf / dsc->drm->slice_count;
> +
> +			reg = dsc->bytes_per_pkt << 16;
> +			reg |= (0x0b << 8);    /* dtype of compressed image */
> +
> +			/* pkt_per_line:
> +			 * 0 == 1 pkt
> +			 * 1 == 2 pkt
> +			 * 2 == 4 pkt
> +			 * 3 pkt is not supported
> +			 * above translates to ffs() - 1
> +			 */
> +			reg |= (ffs(dsc->pkt_per_line) - 1) << 6;
> +
> +			dsc->eol_byte_num = total_bytes_per_intf % 3;

This was already calculated and assigned just a couple lines above.

> +			reg |= dsc->eol_byte_num << 4;
> +			reg |= 1;

Note that the XML register file exists to map out the layout of these
registers, including bit offset, size, and (enum) constant values.  It
is appreciated if you can replace all these magical shifts and magic
flags/bits with the appropriate enum constants and constructor
functions, after mapping them out in the XML file.

> +
> +			dsi_write(msm_host,
> +				  REG_DSI_VIDEO_COMPRESSION_MODE_CTRL, reg);
> +		}
> +
>  		dsi_write(msm_host, REG_DSI_ACTIVE_H,
>  			DSI_ACTIVE_H_START(ha_start) |
>  			DSI_ACTIVE_H_END(ha_end));
> @@ -959,8 +1034,40 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
>  			DSI_ACTIVE_VSYNC_VPOS_START(vs_start) |
>  			DSI_ACTIVE_VSYNC_VPOS_END(vs_end));
>  	} else {		/* command mode */
> +		if (msm_host->dsc) {
> +			struct msm_display_dsc_config *dsc = msm_host->dsc;
> +			u32 reg, reg_ctrl, reg_ctrl2;
> +			u32 slice_per_intf, bytes_in_slice, total_bytes_per_intf;
> +
> +			reg_ctrl = dsi_read(msm_host, REG_DSI_COMMAND_COMPRESSION_MODE_CTRL);
> +			reg_ctrl2 = dsi_read(msm_host, REG_DSI_COMMAND_COMPRESSION_MODE_CTRL2);

Shouldn't old values be masked out first, before writing new bits or
values below?  The video-mode variant doesn't read back old register
values.

> +
> +			slice_per_intf = DIV_ROUND_UP(hdisplay, dsc->drm->slice_width);
> +			bytes_in_slice = DIV_ROUND_UP(dsc->drm->slice_width *
> +						      dsc->drm->bits_per_pixel, 8);
> +			dsc->drm->slice_chunk_size = bytes_in_slice;
> +			total_bytes_per_intf = dsc->bytes_in_slice * slice_per_intf;
> +			dsc->pkt_per_line = slice_per_intf / dsc->drm->slice_count;
> +
> +			reg = 0x39 << 8;

Same comment about moving magic constants and shifts into the XML file.

> +			reg |= ffs(dsc->pkt_per_line) << 6;

Doesn't the calculation need -1 here just like video mode?

Thanks!

- Marijn

> +
> +			dsc->eol_byte_num = total_bytes_per_intf % 3;
> +			reg |= dsc->eol_byte_num << 4;
> +			reg |= 1;
> +
> +			reg_ctrl |= reg;
> +			reg_ctrl2 |= bytes_in_slice;
> +
> +			dsi_write(msm_host, REG_DSI_COMMAND_COMPRESSION_MODE_CTRL, reg);
> +			dsi_write(msm_host, REG_DSI_COMMAND_COMPRESSION_MODE_CTRL2, reg_ctrl2);
> +		}
> +
>  		/* image data and 1 byte write_memory_start cmd */
> -		wc = hdisplay * dsi_get_bpp(msm_host->format) / 8 + 1;
> +		if (!msm_host->dsc)
> +			wc = hdisplay * dsi_get_bpp(msm_host->format) / 8 + 1;
> +		else
> +			wc = mode->hdisplay / 2 + 1;
>  
>  		dsi_write(msm_host, REG_DSI_CMD_MDP_STREAM0_CTRL,
>  			DSI_CMD_MDP_STREAM0_CTRL_WORD_COUNT(wc) |
> @@ -2051,9 +2158,13 @@ int msm_dsi_host_modeset_init(struct mipi_dsi_host *host,
>  {
>  	struct msm_dsi_host *msm_host = to_msm_dsi_host(host);
>  	const struct msm_dsi_cfg_handler *cfg_hnd = msm_host->cfg_hnd;
> +	struct msm_drm_private *priv;
>  	int ret;
>  
>  	msm_host->dev = dev;
> +	priv = dev->dev_private;
> +	priv->dsc = msm_host->dsc;
> +
>  	ret = cfg_hnd->ops->tx_buf_alloc(msm_host, SZ_4K);
>  	if (ret) {
>  		pr_err("%s: alloc tx gem obj failed, %d\n", __func__, ret);
> -- 
> 2.31.1
> 

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