Re: [PATCH V5 5/6] drm: bridge: samsung-dsim: Dynamically configure DPHY timing

From: Adam Ford
Date: Fri May 12 2023 - 16:01:19 EST

On Fri, May 12, 2023 at 2:37 PM Lucas Stach <l.stach@xxxxxxxxxxxxxx> wrote:
>
> Hi Adam,
>
> Am Samstag, dem 06.05.2023 um 14:24 -0500 schrieb Adam Ford:
> > The DPHY timings are currently hard coded. Since the input
> > clock can be variable, the phy timings need to be variable
> > too. Add an additional variable to the driver data to enable
> > this feature to prevent breaking boards that don't support it.
> >
> > The phy_mipi_dphy_get_default_config function configures the
> > DPHY timings in pico-seconds, and a small macro converts those
> > timings into clock cycles based on the pixel clock rate.
> >
> This week I finally had some time to take a deeper look at this series
> and test it on some of my systems.

Thanks for testing this!
>
> This patch causes issues when the burst clock rate is fixed by
> supplying the DT entry. Instead of describing the issue below, I'm
> attaching the patch that makes things work on my system.

Oops, sorry about that.

>
> I would appreciate if you could test this one on your side. Feel free
> to squash it into yours if you find it working properly.

I reviewed your patch, and it looks like it makes a lot of sense.
If it works, I'll squash them together and add your name to the sign-off.

>
> Also I would almost bet that dynamic_dphy is working on the Exynos
> boards with that fix added. So if anyone with access to those boards
> would like to give it a shot, we may be able to get rid of the
> hardcoded PHY parameters altogether, which would be a nice cleanup.

I wondered the same thing, but I didn't want to create more work for
Marek S and since there was so much churn getting the original driver
ported, I thought it would be the safest thing to try to give the
imx8m m/n/p the features without breaking the Exynos.

Marek S - Do you want me to post this file without the extra checks to
see if it still works with Exynos?

adam
>
> Regards,
> Lucas
>
> > Signed-off-by: Adam Ford <aford173@xxxxxxxxx>
> > Tested-by: Chen-Yu Tsai <wenst@xxxxxxxxxxxx>
> > Tested-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
> > Reviewed-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
> > Tested-by: Michael Walle <michael@xxxxxxxx>
> > ---
> > drivers/gpu/drm/bridge/samsung-dsim.c | 74 ++++++++++++++++++++++++---
> > include/drm/bridge/samsung-dsim.h | 1 +
> > 2 files changed, 68 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> > index 08266303c261..d19a5c87b749 100644
> > --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> > +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> > @@ -218,6 +218,8 @@
> >
> > #define OLD_SCLK_MIPI_CLK_NAME "pll_clk"
> >
> > +#define PS_TO_CYCLE(ps, hz) DIV64_U64_ROUND_CLOSEST(((ps) * (hz)), 1000000000000ULL)
> > +
> > static const char *const clk_names[5] = {
> > "bus_clk",
> > "sclk_mipi",
> > @@ -487,6 +489,7 @@ static const struct samsung_dsim_driver_data imx8mm_dsi_driver_data = {
> > .m_min = 64,
> > .m_max = 1023,
> > .min_freq = 1050,
> > + .dynamic_dphy = 1,
> > };
> >
> > static const struct samsung_dsim_driver_data *
> > @@ -698,13 +701,50 @@ static void samsung_dsim_set_phy_ctrl(struct samsung_dsim *dsi)
> > const struct samsung_dsim_driver_data *driver_data = dsi->driver_data;
> > const unsigned int *reg_values = driver_data->reg_values;
> > u32 reg;
> > + struct drm_display_mode *m = &dsi->mode;
> > + int bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
> > + struct phy_configure_opts_mipi_dphy cfg;
> > + int clk_prepare, lpx, clk_zero, clk_post, clk_trail;
> > + int hs_exit, hs_prepare, hs_zero, hs_trail;
> > + unsigned long long clock_in_hz = m->clock * 1000;
> >
> > if (driver_data->has_freqband)
> > return;
> >
> > + /* The dynamic_phy has the ability to adjust PHY Timing settings */
> > + if (driver_data->dynamic_dphy) {
> > + phy_mipi_dphy_get_default_config(clock_in_hz, bpp, dsi->lanes, &cfg);
> > +
> > + /*
> > + * TODO:
> > + * The tech reference manual for i.MX8M Mini/Nano/Plus
> > + * doesn't state what the definition of the PHYTIMING
> > + * bits are beyond their address and bit position.
> > + * After reviewing NXP's downstream code, it appears
> > + * that the various PHYTIMING registers take the number
> > + * of cycles and use various dividers on them. This
> > + * calculation does not result in an exact match to the
> > + * downstream code, but it is very close, and it appears
> > + * to sync at a variety of resolutions. If someone
> > + * can get a more accurate mathematical equation needed
> > + * for these registers, this should be updated.
> > + */
> > +
> > + lpx = PS_TO_CYCLE(cfg.lpx, clock_in_hz);
> > + hs_exit = PS_TO_CYCLE(cfg.hs_exit, clock_in_hz);
> > + clk_prepare = PS_TO_CYCLE(cfg.clk_prepare, clock_in_hz);
> > + clk_zero = PS_TO_CYCLE(cfg.clk_zero, clock_in_hz);
> > + clk_post = PS_TO_CYCLE(cfg.clk_post, clock_in_hz);
> > + clk_trail = PS_TO_CYCLE(cfg.clk_trail, clock_in_hz);
> > + hs_prepare = PS_TO_CYCLE(cfg.hs_prepare, clock_in_hz);
> > + hs_zero = PS_TO_CYCLE(cfg.hs_zero, clock_in_hz);
> > + hs_trail = PS_TO_CYCLE(cfg.hs_trail, clock_in_hz);
> > + }
> > +
> > /* B D-PHY: D-PHY Master & Slave Analog Block control */
> > reg = reg_values[PHYCTRL_ULPS_EXIT] | reg_values[PHYCTRL_VREG_LP] |
> > reg_values[PHYCTRL_SLEW_UP];
> > +
> > samsung_dsim_write(dsi, DSIM_PHYCTRL_REG, reg);
> >
> > /*
> > @@ -712,7 +752,11 @@ static void samsung_dsim_set_phy_ctrl(struct samsung_dsim *dsi)
> > * T HS-EXIT: Time that the transmitter drives LP-11 following a HS
> > * burst
> > */
> > - reg = reg_values[PHYTIMING_LPX] | reg_values[PHYTIMING_HS_EXIT];
> > + if (driver_data->dynamic_dphy)
> > + reg = DSIM_PHYTIMING_LPX(lpx) | DSIM_PHYTIMING_HS_EXIT(hs_exit);
> > + else
> > + reg = reg_values[PHYTIMING_LPX] | reg_values[PHYTIMING_HS_EXIT];
> > +
> > samsung_dsim_write(dsi, DSIM_PHYTIMING_REG, reg);
> >
> > /*
> > @@ -728,10 +772,17 @@ static void samsung_dsim_set_phy_ctrl(struct samsung_dsim *dsi)
> > * T CLK-TRAIL: Time that the transmitter drives the HS-0 state after
> > * the last payload clock bit of a HS transmission burst
> > */
> > - reg = reg_values[PHYTIMING_CLK_PREPARE] |
> > - reg_values[PHYTIMING_CLK_ZERO] |
> > - reg_values[PHYTIMING_CLK_POST] |
> > - reg_values[PHYTIMING_CLK_TRAIL];
> > + if (driver_data->dynamic_dphy) {
> > + reg = DSIM_PHYTIMING1_CLK_PREPARE(clk_prepare) |
> > + DSIM_PHYTIMING1_CLK_ZERO(clk_zero) |
> > + DSIM_PHYTIMING1_CLK_POST(clk_post) |
> > + DSIM_PHYTIMING1_CLK_TRAIL(clk_trail);
> > + } else {
> > + reg = reg_values[PHYTIMING_CLK_PREPARE] |
> > + reg_values[PHYTIMING_CLK_ZERO] |
> > + reg_values[PHYTIMING_CLK_POST] |
> > + reg_values[PHYTIMING_CLK_TRAIL];
> > + }
> >
> > samsung_dsim_write(dsi, DSIM_PHYTIMING1_REG, reg);
> >
> > @@ -744,8 +795,17 @@ static void samsung_dsim_set_phy_ctrl(struct samsung_dsim *dsi)
> > * T HS-TRAIL: Time that the transmitter drives the flipped differential
> > * state after last payload data bit of a HS transmission burst
> > */
> > - reg = reg_values[PHYTIMING_HS_PREPARE] | reg_values[PHYTIMING_HS_ZERO] |
> > - reg_values[PHYTIMING_HS_TRAIL];
> > +
> > + if (driver_data->dynamic_dphy) {
> > + reg = DSIM_PHYTIMING2_HS_PREPARE(hs_prepare) |
> > + DSIM_PHYTIMING2_HS_ZERO(hs_zero) |
> > + DSIM_PHYTIMING2_HS_TRAIL(hs_trail);
> > + } else {
> > + reg = reg_values[PHYTIMING_HS_PREPARE] |
> > + reg_values[PHYTIMING_HS_ZERO] |
> > + reg_values[PHYTIMING_HS_TRAIL];
> > + }
> > +
> > samsung_dsim_write(dsi, DSIM_PHYTIMING2_REG, reg);
> > }
> >
> > diff --git a/include/drm/bridge/samsung-dsim.h b/include/drm/bridge/samsung-dsim.h
> > index a1a5b2b89a7a..76ea8a1720cc 100644
> > --- a/include/drm/bridge/samsung-dsim.h
> > +++ b/include/drm/bridge/samsung-dsim.h
> > @@ -62,6 +62,7 @@ struct samsung_dsim_driver_data {
> > const unsigned int *reg_values;
> > u16 m_min;
> > u16 m_max;
> > + bool dynamic_dphy;
> > };
> >
> > struct samsung_dsim_host_ops {
>