Re: [PATCH v7 2/2] drm/bridge: anx7625: Add anx7625 MIPI DSI/DPI to DP bridge driver

[Nicolas Boichat <drinkcat@chromium.org>]

Hi,

Just commenting on the mode_fixup function that was added in v7.

On Tue, Feb 25, 2020 at 2:15 PM Xin Ji <xji@analogixsemi.com> wrote:
>
> The ANX7625 is an ultra-low power 4K Mobile HD Transmitter designed
> for portable device. It converts MIPI DSI/DPI to DisplayPort 1.3 4K.
>
> The ANX7625 can support both USB Type-C PD feature and MIPI DSI/DPI
> to DP feature. This driver only enabled MIPI DSI/DPI to DP feature.
>
> Signed-off-by: Xin Ji <xji@analogixsemi.com>
> ---
>  drivers/gpu/drm/bridge/Makefile           |    2 +-
>  drivers/gpu/drm/bridge/analogix/Kconfig   |    6 +
>  drivers/gpu/drm/bridge/analogix/Makefile  |    1 +
>  drivers/gpu/drm/bridge/analogix/anx7625.c | 2172 +++++++++++++++++++++++++++++
>  drivers/gpu/drm/bridge/analogix/anx7625.h |  410 ++++++
>  5 files changed, 2590 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/gpu/drm/bridge/analogix/anx7625.c
>  create mode 100644 drivers/gpu/drm/bridge/analogix/anx7625.h
>
> diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
> index 4934fcf..bcd388a 100644
> --- a/drivers/gpu/drm/bridge/Makefile
> +++ b/drivers/gpu/drm/bridge/Makefile
[snip]
> +static bool anx7625_bridge_mode_fixup(struct drm_bridge *bridge,
> +                                     const struct drm_display_mode *mode,
> +                                     struct drm_display_mode *adj)
> +{
> +       struct anx7625_data *ctx = bridge_to_anx7625(bridge);
> +       struct device *dev = &ctx->client->dev;
> +       u32 hsync, hfp, hbp, hactive, hblanking;
> +       u32 adj_hsync, adj_hfp, adj_hbp, adj_hblanking, delta_adj;
> +       u32 vref, adj_clock;
> +
> +       DRM_DEV_DEBUG_DRIVER(dev, "drm mode fixup set\n");
> +
> +       mutex_lock(&ctx->lock);

Why do you need this lock?

> +
> +       hactive = mode->hdisplay;

This is never used, drop it?

> +       hsync = mode->hsync_end - mode->hsync_start;
> +       hfp = mode->hsync_start - mode->hdisplay;
> +       hbp = mode->htotal - mode->hsync_end;
> +       hblanking = mode->htotal - mode->hdisplay;
> +
> +       DRM_DEV_DEBUG_DRIVER(dev, "before mode fixup\n");
> +       DRM_DEV_DEBUG_DRIVER(dev, "hsync(%d),hfp(%d),hbp(%d),clock(%d)\n",
> +                            hsync,
> +                            hfp,
> +                            hbp,
> +                            adj->clock);
> +       DRM_DEV_DEBUG_DRIVER(dev, "hsync_start(%d),hsync_end(%d),htotal(%d)\n",
> +                            adj->hsync_start,
> +                            adj->hsync_end,
> +                            adj->htotal);
> +
> +       adj_hfp = hfp;
> +       adj_hsync = hsync;
> +       adj_hbp = hbp;
> +       adj_hblanking = hblanking;
> +
> +       /* plus 1 if hfp is odd */

A better way to word these comments is to say "hfp needs to be even",
otherwise, you're just repeating what we can already see in the code.

> +       if (hfp & 0x1) {
> +               adj_hfp = hfp + 1;

adj_hfp -= 1 for consistency?

> +               adj_hblanking += 1;
> +       }
> +
> +       /* minus 1 if hbp is odd */
> +       if (hbp & 0x1) {
> +               adj_hbp = hbp - 1;

ditto, adj_hbp -= 1;

> +               adj_hblanking -= 1;
> +       }
> +
> +       /* plus 1 if hsync is odd */
> +       if (hsync & 0x1) {
> +               if (adj_hblanking < hblanking)
> +                       adj_hsync = hsync + 1;

ditto

> +               else
> +                       adj_hsync = hsync - 1;

ditto

> +       }
> +
> +       /*
> +        * once illegal timing detected, use default HFP, HSYNC, HBP
> +        */
> +       if (hblanking < HBLANKING_MIN || (hfp < HP_MIN && hbp < HP_MIN)) {

should this be adj_hblanking/adj_hfp/adj_hbp?

> +               adj_hsync = SYNC_LEN_DEF;
> +               adj_hfp = HFP_HBP_DEF;
> +               adj_hbp = HFP_HBP_DEF;
> +               vref = adj->clock * 1000 / (adj->htotal * adj->vtotal);
> +               if (hblanking < HBLANKING_MIN) {
> +                       delta_adj = HBLANKING_MIN - hblanking;
> +                       adj_clock = vref * delta_adj * adj->vtotal;
> +                       adj->clock += DIV_ROUND_UP(adj_clock, 1000);
> +               } else {
> +                       delta_adj = hblanking - HBLANKING_MIN;
> +                       adj_clock = vref * delta_adj * adj->vtotal;
> +                       adj->clock -= DIV_ROUND_UP(adj_clock, 1000);
> +               }
> +
> +               DRM_WARN("illegal hblanking timing, use default.\n");
> +               DRM_WARN("hfp(%d),hbp(%d),hsync(%d).\n", hfp, hbp, hsync);

How likely is it that this mode is going to work? Can you just return
false here to reject the mode?

> +       } else if (adj_hfp < HP_MIN) {
> +               /* adjust hfp if hfp less than HP_MIN */
> +               delta_adj = HP_MIN - adj_hfp;
> +               adj_hfp = HP_MIN;
> +
> +               /*
> +                * balance total HBlanking pixel, if HBP hasn't enough space,

"does not have enough space"

> +                * adjust HSYNC length, otherwize adjust HBP

otherwise

> +                */
> +               if ((adj_hbp - delta_adj) < HP_MIN)
> +                       /* hbp not enough space */
> +                       adj_hsync -= delta_adj;
> +               else
> +                       adj_hbp -= delta_adj;
> +       } else if (adj_hbp < HP_MIN) {
> +               delta_adj = HP_MIN - adj_hbp;
> +               adj_hbp = HP_MIN;
> +
> +               /*
> +                * balance total HBlanking pixel, if HBP hasn't enough space,
> +                * adjust HSYNC length, otherwize adjust HBP
> +                */
> +               if ((adj_hfp - delta_adj) < HP_MIN)
> +                       /* hbp not enough space */
> +                       adj_hsync -= delta_adj;
> +               else
> +                       adj_hfp -= delta_adj;
> +       }
> +
> +       DRM_DEV_DEBUG_DRIVER(dev, "after mode fixup\n");
> +       DRM_DEV_DEBUG_DRIVER(dev, "hsync(%d),hfp(%d),hbp(%d),clock(%d)\n",

Add spaces after commas in your debug strings (same above and below).

> +                            adj_hsync,
> +                            adj_hfp,
> +                            adj_hbp,
> +                            adj->clock);

Put these 4 on a single line.

> +
> +       /* reconstruct timing */
> +       adj->hsync_start = adj->hdisplay + adj_hfp;
> +       adj->hsync_end = adj->hsync_start + adj_hsync;
> +       adj->htotal = adj->hsync_end + adj_hbp;
> +       DRM_DEV_DEBUG_DRIVER(dev, "hsync_start(%d),hsync_end(%d),htotal(%d)\n",
> +                            adj->hsync_start,
> +                            adj->hsync_end,
> +                            adj->htotal);
> +
> +       mutex_unlock(&ctx->lock);
> +
> +       return true;
> +}
> +
> [snip]