Re: [PATCH 3/5] drm/msm/dsi: Account for DSC's bits_per_pixel having 4 fractional bits
From: Dmitry Baryshkov
Date: Tue Oct 04 2022 - 18:40:25 EST
On 05/10/2022 01:35, Marijn Suijten wrote:
On 2022-10-04 17:45:50, Dmitry Baryshkov wrote:
On Sat, 1 Oct 2022 at 22:08, Marijn Suijten
<marijn.suijten@xxxxxxxxxxxxxx> wrote:
[..]
- bytes_in_slice = DIV_ROUND_UP(dsc->slice_width * dsc->bits_per_pixel, 8);
+ bytes_in_slice = DIV_ROUND_UP(dsc->slice_width * bpp, 8);
bytes_in_slice = DIV_ROUND_UP(dsc->slice_width * dsc->bits_per_pixel, 8 * 16); ?
Not necessarily a fan of this, it "hides" the fact that we are dealing
with 4 fractional bits (1/16th precision, it is correct though); but
since this is the only use of `bpp` I can change it and document this
fact wiht a comment on top (including referencing the validation pointed
out in dsi_populate_dsc_params()).
Alternatively we can inline the `>> 4` here?
No, I don't think so. If we shift by 4 bits, we'd loose the fractional
part. DIV_ROUND_UP( .... , 8 * 16) ensures that we round it up rather
than just dropping it.
dsc->slice_chunk_size = bytes_in_slice;
@@ -913,6 +918,7 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
u32 va_end = va_start + mode->vdisplay;
u32 hdisplay = mode->hdisplay;
u32 wc;
+ int ret;
DBG("");
@@ -948,7 +954,9 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
/* we do the calculations for dsc parameters here so that
* panel can use these parameters
*/
- dsi_populate_dsc_params(dsc);
+ ret = dsi_populate_dsc_params(dsc);
+ if (ret)
+ return;
/* Divide the display by 3 but keep back/font porch and
* pulse width same
@@ -1229,6 +1237,10 @@ static int dsi_cmd_dma_add(struct msm_dsi_host *msm_host,
if (packet.size < len)
memset(data + packet.size, 0xff, len - packet.size);
+ if (msg->type == MIPI_DSI_PICTURE_PARAMETER_SET)
+ print_hex_dump(KERN_DEBUG, "ALL:", DUMP_PREFIX_NONE,
+ 16, 1, data, len, false);
+
if (cfg_hnd->ops->tx_buf_put)
cfg_hnd->ops->tx_buf_put(msm_host);
@@ -1786,6 +1798,12 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
int data;
int final_value, final_scale;
int i;
+ int bpp = dsc->bits_per_pixel >> 4;
+
+ if (dsc->bits_per_pixel & 0xf) {
+ pr_err("DSI does not support fractional bits_per_pixel\n");
+ return -EINVAL;
+ }
dsc->rc_model_size = 8192;
dsc->first_line_bpg_offset = 12;
@@ -1807,7 +1825,7 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
}
dsc->initial_offset = 6144; /* Not bpp 12 */
- if (dsc->bits_per_pixel != 8)
+ if (bpp != 8)
dsc->initial_offset = 2048; /* bpp = 12 */
mux_words_size = 48; /* bpc == 8/10 */
@@ -1830,16 +1848,16 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
* params are calculated
*/
groups_per_line = DIV_ROUND_UP(dsc->slice_width, 3);
- dsc->slice_chunk_size = dsc->slice_width * dsc->bits_per_pixel / 8;
- if ((dsc->slice_width * dsc->bits_per_pixel) % 8)
+ dsc->slice_chunk_size = dsc->slice_width * bpp / 8;
+ if ((dsc->slice_width * bpp) % 8)
One can use fixed point math here too:
dsc->slice_chunk_size = (dsc->slice_width * dsc->bits_per_pixel + 8 *
16 - 1)/ (8 * 16);
Good catch, this is effectively a DIV_ROUND_UP() that we happened to
call bytes_in_slice above...
Shall I tackle this in the same patch, or insert another cleanup patch?
It's up to you. I usually prefer separate patches, even if just to ease
bisecting between unrelated changes.
In fact dsi_populate_dsc_params() is called first (this comment),
followed by dsi_update_dsc_timing(), meaning that slice_chunk_size is
already provided and shouldn't be recomputed.
dsc->slice_chunk_size++;
/* rbs-min */
min_rate_buffer_size = dsc->rc_model_size - dsc->initial_offset +
- dsc->initial_xmit_delay * dsc->bits_per_pixel +
+ dsc->initial_xmit_delay * bpp +
groups_per_line * dsc->first_line_bpg_offset;
- hrd_delay = DIV_ROUND_UP(min_rate_buffer_size, dsc->bits_per_pixel);
+ hrd_delay = DIV_ROUND_UP(min_rate_buffer_size, bpp);
dsc->initial_dec_delay = hrd_delay - dsc->initial_xmit_delay;
@@ -1862,7 +1880,7 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
data = 2048 * (dsc->rc_model_size - dsc->initial_offset + num_extra_mux_bits);
dsc->slice_bpg_offset = DIV_ROUND_UP(data, groups_total);
- target_bpp_x16 = dsc->bits_per_pixel * 16;
+ target_bpp_x16 = bpp * 16;
data = (dsc->initial_xmit_delay * target_bpp_x16) / 16;
It looks like this can be replaced with the direct multiplication
instead, maybe with support for overflow/rounding.
Thanks, Abhinav pointed out the same in patch 1/5 which originally
cleaned up most - but apparently not all! - of the math here. I don't
think this value should ever overlow, nor does this `* 16 / 16` have any
effect on rounding (that'd be `/ 16 * 16`).
Ack
final_value = dsc->rc_model_size - data + num_extra_mux_bits;
--
2.37.3
--
With best wishes
Dmitry
--
With best wishes
Dmitry