Re: [PATCH V2 1/6] drm: bridge: samsung-dsim: fix blanking packet size calculation
Am Mittwoch, dem 03.05.2023 um 22:05 +0530 schrieb Jagan Teki:
> On Mon, Apr 24, 2023 at 3:17 PM Adam Ford wrote:
> >
> > On Mon, Apr 24, 2023 at 4:03 AM Jagan Teki
> > wrote:
> > >
> > > On Sun, Apr 23, 2023 at 5:42 PM Adam Ford wrote:
> > > >
> > > > From: Lucas Stach
> > > >
> > > > Scale the blanking packet sizes to match the ratio between HS clock
> > > > and DPI interface clock. The controller seems to do internal scaling
> > > > to the number of active lanes, so we don't take those into account.
> > > >
> > > > Signed-off-by: Lucas Stach
> > > > Signed-off-by: Adam Ford
> > > > ---
> > > > drivers/gpu/drm/bridge/samsung-dsim.c | 18 +++---
> > > > 1 file changed, 15 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c
> > > > b/drivers/gpu/drm/bridge/samsung-dsim.c
> > > > index e0a402a85787..2be3b58624c3 100644
> > > > --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> > > > +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> > > > @@ -874,17 +874,29 @@ static void samsung_dsim_set_display_mode(struct
> > > > samsung_dsim *dsi)
> > > > u32 reg;
> > > >
> > > > if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
> > > > + int byte_clk_khz = dsi->burst_clk_rate / 1000 / 8;
> > > > + int hfp = (m->hsync_start - m->hdisplay) * byte_clk_khz
> > > > / m->clock;
> > >
> > > I do not quite understand why it depends on burst_clk_rate, would you
> > > please explain? does it depends on bpp something like this
> > >
> > > mipi_dsi_pixel_format_to_bpp(format) / 8
> >
> > The pixel clock is currently set to the burst clock rate. Dividing
> > the clock by 1000 gets the pixel clock in KHz, and dividing by 8
> > converts bits to bytes.
> > Later in the series, I change the clock from the burst clock to the
> > cached value returned from samsung_dsim_set_pll.
>
> Okay.
>
> >
> > >
> > > > + int hbp = (m->htotal - m->hsync_end) * byte_clk_khz /
> > > > m->clock;
> > > > + int hsa = (m->hsync_end - m->hsync_start) *
> > > > byte_clk_khz / m->clock;
> > > > +
> > > > + /* remove packet overhead when possible */
> > > > + hfp = max(hfp - 6, 0);
> > > > + hbp = max(hbp - 6, 0);
> > > > + hsa = max(hsa - 6, 0);
> > >
> > > 6 blanking packet overhead here means, 4 bytes + payload + 2 bytes
> > > format? does this packet overhead depends on the respective porch's
> > > like hpf, hbp and hsa has different packet overheads?
> >
> > Lucas might be able to explain this better. However, it does match
> > the values of the downstream NXP kernel, and I tried playing with
> > these values manually, and 6 appeared to be the only number that
> > seemed to work for me too. I abandoned my approach for Lucas'
> > implementation, because it seemed more clear than mine.
> > Maybe Lucas can chime in, since this is really his patch.
>
> Lucan, any inputs?
>
The blanking packets are are MIPI long packets, so 4 byte header,
payload, 2 bytes footer. I experimented with different blanking sizes
and haven't found that it would make any difference. I don't think any
real-world horizontal blanking sizes would require multiple packets to
be sent.
Regards,
Lucas
Re: [PATCH V2 1/6] drm: bridge: samsung-dsim: fix blanking packet size calculation
On Mon, Apr 24, 2023 at 3:17 PM Adam Ford wrote:
>
> On Mon, Apr 24, 2023 at 4:03 AM Jagan Teki wrote:
> >
> > On Sun, Apr 23, 2023 at 5:42 PM Adam Ford wrote:
> > >
> > > From: Lucas Stach
> > >
> > > Scale the blanking packet sizes to match the ratio between HS clock
> > > and DPI interface clock. The controller seems to do internal scaling
> > > to the number of active lanes, so we don't take those into account.
> > >
> > > Signed-off-by: Lucas Stach
> > > Signed-off-by: Adam Ford
> > > ---
> > > drivers/gpu/drm/bridge/samsung-dsim.c | 18 +++---
> > > 1 file changed, 15 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c
> > > b/drivers/gpu/drm/bridge/samsung-dsim.c
> > > index e0a402a85787..2be3b58624c3 100644
> > > --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> > > +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> > > @@ -874,17 +874,29 @@ static void samsung_dsim_set_display_mode(struct
> > > samsung_dsim *dsi)
> > > u32 reg;
> > >
> > > if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
> > > + int byte_clk_khz = dsi->burst_clk_rate / 1000 / 8;
> > > + int hfp = (m->hsync_start - m->hdisplay) * byte_clk_khz /
> > > m->clock;
> >
> > I do not quite understand why it depends on burst_clk_rate, would you
> > please explain? does it depends on bpp something like this
> >
> > mipi_dsi_pixel_format_to_bpp(format) / 8
>
> The pixel clock is currently set to the burst clock rate. Dividing
> the clock by 1000 gets the pixel clock in KHz, and dividing by 8
> converts bits to bytes.
> Later in the series, I change the clock from the burst clock to the
> cached value returned from samsung_dsim_set_pll.
Okay.
>
> >
> > > + int hbp = (m->htotal - m->hsync_end) * byte_clk_khz /
> > > m->clock;
> > > + int hsa = (m->hsync_end - m->hsync_start) * byte_clk_khz
> > > / m->clock;
> > > +
> > > + /* remove packet overhead when possible */
> > > + hfp = max(hfp - 6, 0);
> > > + hbp = max(hbp - 6, 0);
> > > + hsa = max(hsa - 6, 0);
> >
> > 6 blanking packet overhead here means, 4 bytes + payload + 2 bytes
> > format? does this packet overhead depends on the respective porch's
> > like hpf, hbp and hsa has different packet overheads?
>
> Lucas might be able to explain this better. However, it does match
> the values of the downstream NXP kernel, and I tried playing with
> these values manually, and 6 appeared to be the only number that
> seemed to work for me too. I abandoned my approach for Lucas'
> implementation, because it seemed more clear than mine.
> Maybe Lucas can chime in, since this is really his patch.
Lucan, any inputs?
Jagan.
Re: [PATCH V2 1/6] drm: bridge: samsung-dsim: fix blanking packet size calculation
On Mon, Apr 24, 2023 at 4:03 AM Jagan Teki wrote:
>
> On Sun, Apr 23, 2023 at 5:42 PM Adam Ford wrote:
> >
> > From: Lucas Stach
> >
> > Scale the blanking packet sizes to match the ratio between HS clock
> > and DPI interface clock. The controller seems to do internal scaling
> > to the number of active lanes, so we don't take those into account.
> >
> > Signed-off-by: Lucas Stach
> > Signed-off-by: Adam Ford
> > ---
> > drivers/gpu/drm/bridge/samsung-dsim.c | 18 +++---
> > 1 file changed, 15 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c
> > b/drivers/gpu/drm/bridge/samsung-dsim.c
> > index e0a402a85787..2be3b58624c3 100644
> > --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> > +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> > @@ -874,17 +874,29 @@ static void samsung_dsim_set_display_mode(struct
> > samsung_dsim *dsi)
> > u32 reg;
> >
> > if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
> > + int byte_clk_khz = dsi->burst_clk_rate / 1000 / 8;
> > + int hfp = (m->hsync_start - m->hdisplay) * byte_clk_khz /
> > m->clock;
>
> I do not quite understand why it depends on burst_clk_rate, would you
> please explain? does it depends on bpp something like this
>
> mipi_dsi_pixel_format_to_bpp(format) / 8
The pixel clock is currently set to the burst clock rate. Dividing
the clock by 1000 gets the pixel clock in KHz, and dividing by 8
converts bits to bytes.
Later in the series, I change the clock from the burst clock to the
cached value returned from samsung_dsim_set_pll.
>
> > + int hbp = (m->htotal - m->hsync_end) * byte_clk_khz /
> > m->clock;
> > + int hsa = (m->hsync_end - m->hsync_start) * byte_clk_khz /
> > m->clock;
> > +
> > + /* remove packet overhead when possible */
> > + hfp = max(hfp - 6, 0);
> > + hbp = max(hbp - 6, 0);
> > + hsa = max(hsa - 6, 0);
>
> 6 blanking packet overhead here means, 4 bytes + payload + 2 bytes
> format? does this packet overhead depends on the respective porch's
> like hpf, hbp and hsa has different packet overheads?
Lucas might be able to explain this better. However, it does match
the values of the downstream NXP kernel, and I tried playing with
these values manually, and 6 appeared to be the only number that
seemed to work for me too. I abandoned my approach for Lucas'
implementation, because it seemed more clear than mine.
Maybe Lucas can chime in, since this is really his patch.
adam
>
> Jagan.
Re: [PATCH V2 1/6] drm: bridge: samsung-dsim: fix blanking packet size calculation
On Sun, Apr 23, 2023 at 5:42 PM Adam Ford wrote:
>
> From: Lucas Stach
>
> Scale the blanking packet sizes to match the ratio between HS clock
> and DPI interface clock. The controller seems to do internal scaling
> to the number of active lanes, so we don't take those into account.
>
> Signed-off-by: Lucas Stach
> Signed-off-by: Adam Ford
> ---
> drivers/gpu/drm/bridge/samsung-dsim.c | 18 +++---
> 1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c
> b/drivers/gpu/drm/bridge/samsung-dsim.c
> index e0a402a85787..2be3b58624c3 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -874,17 +874,29 @@ static void samsung_dsim_set_display_mode(struct
> samsung_dsim *dsi)
> u32 reg;
>
> if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
> + int byte_clk_khz = dsi->burst_clk_rate / 1000 / 8;
> + int hfp = (m->hsync_start - m->hdisplay) * byte_clk_khz /
> m->clock;
I do not quite understand why it depends on burst_clk_rate, would you
please explain? does it depends on bpp something like this
mipi_dsi_pixel_format_to_bpp(format) / 8
> + int hbp = (m->htotal - m->hsync_end) * byte_clk_khz /
> m->clock;
> + int hsa = (m->hsync_end - m->hsync_start) * byte_clk_khz /
> m->clock;
> +
> + /* remove packet overhead when possible */
> + hfp = max(hfp - 6, 0);
> + hbp = max(hbp - 6, 0);
> + hsa = max(hsa - 6, 0);
6 blanking packet overhead here means, 4 bytes + payload + 2 bytes
format? does this packet overhead depends on the respective porch's
like hpf, hbp and hsa has different packet overheads?
Jagan.
