Re: [PATCH v3 8/9] drm/bridge: ti-sn65dsi86: Train at faster rates if slower ones fail

Bjorn Andersson
2020-02-03T23:41:11Z

On Wed 18 Dec 14:35 PST 2019, Douglas Anderson wrote:

> If we fail training at a lower DP link rate let's now keep trying
> until we run out of rates to try. Basically the algorithm here is to
> start at the link rate that is the theoretical minimum and then slowly
> bump up until we run out of rates or hit the max rate of the sink. We
> query the sink using a DPCD read.
>
> This is, in fact, important in practice. Specifically at least one
> panel hooked up to the bridge (AUO B116XAK01) had a theoretical min
> rate more than 1.62 GHz (if run at 24 bpp) and fails to train at the
> next rate (2.16 GHz). It would train at 2.7 GHz, though.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Tested-by: Rob Clark <robdclark@gmail.com>
> Reviewed-by: Rob Clark <robdclark@gmail.com>

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

> ---
>
> Changes in v3: None
> Changes in v2:
> - Squash in maybe-uninitialized fix from Rob Clark.
>
> drivers/gpu/drm/bridge/ti-sn65dsi86.c | 71 ++++++++++++++++++++++-----
> 1 file changed, 60 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index 48fb4dc72e1c..e1b817ccd9c7 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -454,7 +454,7 @@ static const unsigned int ti_sn_bridge_dp_rate_lut[] = {
> 0, 1620, 2160, 2430, 2700, 3240, 4320, 5400
> };
>
> -static void ti_sn_bridge_set_dp_rate(struct ti_sn_bridge *pdata)
> +static int ti_sn_bridge_calc_min_dp_rate_idx(struct ti_sn_bridge *pdata)
> {
> unsigned int bit_rate_khz, dp_rate_mhz;
> unsigned int i;
> @@ -472,8 +472,42 @@ static void ti_sn_bridge_set_dp_rate(struct ti_sn_bridge *pdata)
> if (ti_sn_bridge_dp_rate_lut[i] > dp_rate_mhz)
> break;
>
> - regmap_update_bits(pdata->regmap, SN_DATARATE_CONFIG_REG,
> - DP_DATARATE_MASK, DP_DATARATE(i));
> + return i;
> +}
> +
> +static int ti_sn_bridge_get_max_dp_rate_idx(struct ti_sn_bridge *pdata)
> +{
> + u8 data;
> + int ret;
> +
> + ret = drm_dp_dpcd_readb(&pdata->aux, DP_MAX_LINK_RATE, &data);
> + if (ret != 1) {
> + DRM_DEV_ERROR(pdata->dev,
> + "Can't read max rate (%d); assuming 5.4 GHz\n",
> + ret);
> + return ARRAY_SIZE(ti_sn_bridge_dp_rate_lut) - 1;
> + }
> +
> + /*
> + * Return an index into ti_sn_bridge_dp_rate_lut. Just hardcode
> + * these indicies since it's not like the register spec is ever going
> + * to change and a loop would just be more complicated. Apparently
> + * the DP sink can only return these few rates as supported even
> + * though the bridge allows some rates in between.
> + */
> + switch (data) {
> + case DP_LINK_BW_1_62:
> + return 1;
> + case DP_LINK_BW_2_7:
> + return 4;
> + case DP_LINK_BW_5_4:
> + return 7;
> + }
> +
> + DRM_DEV_ERROR(pdata->dev,
> + "Unexpected max data rate (%#x); assuming 5.4 GHz\n",
> + (int)data);
> + return ARRAY_SIZE(ti_sn_bridge_dp_rate_lut) - 1;
> }
>
> static void ti_sn_bridge_set_video_timings(struct ti_sn_bridge *pdata)
> @@ -530,13 +564,15 @@ static unsigned int ti_sn_get_max_lanes(struct ti_sn_bridge *pdata)
> return data & DP_LANE_COUNT_MASK;
> }
>
> -static int ti_sn_link_training(struct ti_sn_bridge *pdata)
> +static int ti_sn_link_training(struct ti_sn_bridge *pdata, int dp_rate_idx,
> + const char **last_err_str)
> {
> unsigned int val;
> int ret;
>
> /* set dp clk frequency value */
> - ti_sn_bridge_set_dp_rate(pdata);
> + regmap_update_bits(pdata->regmap, SN_DATARATE_CONFIG_REG,
> + DP_DATARATE_MASK, DP_DATARATE(dp_rate_idx));
>
> /* enable DP PLL */
> regmap_write(pdata->regmap, SN_PLL_ENABLE_REG, 1);
> @@ -545,7 +581,7 @@ static int ti_sn_link_training(struct ti_sn_bridge *pdata)
> val & DPPLL_SRC_DP_PLL_LOCK, 1000,
> 50 * 1000);
> if (ret) {
> - DRM_ERROR("DP_PLL_LOCK polling failed (%d)\n", ret);
> + *last_err_str = "DP_PLL_LOCK polling failed";
> goto exit;
> }
>
> @@ -556,9 +592,9 @@ static int ti_sn_link_training(struct ti_sn_bridge *pdata)
> val == ML_TX_NORMAL_MODE, 1000,
> 500 * 1000);
> if (ret) {
> - DRM_ERROR("Training complete polling failed (%d)\n", ret);
> + *last_err_str = "Training complete polling failed";
> } else if (val == ML_TX_MAIN_LINK_OFF) {
> - DRM_ERROR("Link training failed, link is off\n");
> + *last_err_str = "Link training failed, link is off";
> ret = -EIO;
> }
>
> @@ -573,8 +609,11 @@ static int ti_sn_link_training(struct ti_sn_bridge *pdata)
> static void ti_sn_bridge_enable(struct drm_bridge *bridge)
> {
> struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge);
> + const char *last_err_str = "No supported DP rate";
> + int dp_rate_idx;
> + int max_dp_rate_idx;
> unsigned int val;
> - int ret;
> + int ret = -EINVAL;
>
> /*
> * Run with the maximum number of lanes that the DP sink supports.
> @@ -616,9 +655,19 @@ static void ti_sn_bridge_enable(struct drm_bridge *bridge)
> regmap_update_bits(pdata->regmap, SN_SSC_CONFIG_REG, DP_NUM_LANES_MASK,
> val);
>
> - ret = ti_sn_link_training(pdata);
> - if (ret)
> + /* Train until we run out of rates */
> + max_dp_rate_idx = ti_sn_bridge_get_max_dp_rate_idx(pdata);
> + for (dp_rate_idx = ti_sn_bridge_calc_min_dp_rate_idx(pdata);
> + dp_rate_idx <= max_dp_rate_idx;
> + dp_rate_idx++) {
> + ret = ti_sn_link_training(pdata, dp_rate_idx, &last_err_str);
> + if (!ret)
> + break;
> + }
> + if (ret) {
> + DRM_DEV_ERROR(pdata->dev, "%s (%d)\n", last_err_str, ret);
> return;
> + }
>
> /* config video parameters */
> ti_sn_bridge_set_video_timings(pdata);
> --
> 2.24.1.735.g03f4e72817-goog
>