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SubjectRe: [PATCH v3 9/9] drm/bridge: ti-sn65dsi86: Avoid invalid rates
On Wed 18 Dec 14:35 PST 2019, Douglas Anderson wrote:

> Based on work by Bjorn Andersson <bjorn.andersson@linaro.org>,
> Jeffrey Hugo <jeffrey.l.hugo@gmail.com>, and
> Rob Clark <robdclark@chromium.org>.
>
> Let's read the SUPPORTED_LINK_RATES and/or MAX_LINK_RATE (depending on
> the eDP version of the sink) to figure out what eDP rates are
> supported and pick the ideal one.
>
> NOTE: I have only personally tested this code on eDP panels that are
> 1.3 or older. Code reading SUPPORTED_LINK_RATES for DP 1.4+ was
> tested by hacking the code to pretend that a table was there.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

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

> ---
>
> Changes in v3:
> - Init rate_valid table, don't rely on stack being 0 (oops).
> - Rename rate_times_200khz to rate_per_200khz.
> - Loop over the ti_sn_bridge_dp_rate_lut table, making code smaller.
> - Use 'true' instead of 1 for bools.
> - Added note to commit message noting DP 1.4+ isn't well tested.
>
> Changes in v2:
> - Patch ("Avoid invalid rates") replaces ("Skip non-standard DP rates")
>
> drivers/gpu/drm/bridge/ti-sn65dsi86.c | 100 +++++++++++++++++++-------
> 1 file changed, 75 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index e1b817ccd9c7..a57c6108cb1f 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -475,39 +475,85 @@ static int ti_sn_bridge_calc_min_dp_rate_idx(struct ti_sn_bridge *pdata)
> return i;
> }
>
> -static int ti_sn_bridge_get_max_dp_rate_idx(struct ti_sn_bridge *pdata)
> +static void ti_sn_bridge_read_valid_rates(struct ti_sn_bridge *pdata,
> + bool rate_valid[])
> {
> - u8 data;
> + unsigned int rate_per_200khz;
> + unsigned int rate_mhz;
> + u8 dpcd_val;
> int ret;
> + int i, j;
> +
> + ret = drm_dp_dpcd_readb(&pdata->aux, DP_EDP_DPCD_REV, &dpcd_val);
> + if (ret != 1) {
> + DRM_DEV_ERROR(pdata->dev,
> + "Can't read eDP rev (%d), assuming 1.1\n", ret);
> + dpcd_val = DP_EDP_11;
> + }
> +
> + if (dpcd_val >= DP_EDP_14) {
> + /* eDP 1.4 devices must provide a custom table */
> + __le16 sink_rates[DP_MAX_SUPPORTED_RATES];
> +
> + ret = drm_dp_dpcd_read(&pdata->aux, DP_SUPPORTED_LINK_RATES,
> + sink_rates, sizeof(sink_rates));
> +
> + if (ret != sizeof(sink_rates)) {
> + DRM_DEV_ERROR(pdata->dev,
> + "Can't read supported rate table (%d)\n", ret);
> +
> + /* By zeroing we'll fall back to DP_MAX_LINK_RATE. */
> + memset(sink_rates, 0, sizeof(sink_rates));
> + }
> +
> + for (i = 0; i < ARRAY_SIZE(sink_rates); i++) {
> + rate_per_200khz = le16_to_cpu(sink_rates[i]);
> +
> + if (!rate_per_200khz)
> + break;
> +
> + rate_mhz = rate_per_200khz * 200 / 1000;
> + for (j = 0;
> + j < ARRAY_SIZE(ti_sn_bridge_dp_rate_lut);
> + j++) {
> + if (ti_sn_bridge_dp_rate_lut[j] == rate_mhz)
> + rate_valid[j] = true;
> + }
> + }
> +
> + for (i = 0; i < ARRAY_SIZE(ti_sn_bridge_dp_rate_lut); i++) {
> + if (rate_valid[i])
> + return;
> + }
> + DRM_DEV_ERROR(pdata->dev,
> + "No matching eDP rates in table; falling back\n");
> + }
>
> - ret = drm_dp_dpcd_readb(&pdata->aux, DP_MAX_LINK_RATE, &data);
> + /* On older versions best we can do is use DP_MAX_LINK_RATE */
> + ret = drm_dp_dpcd_readb(&pdata->aux, DP_MAX_LINK_RATE, &dpcd_val);
> 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;
> + dpcd_val = DP_LINK_BW_5_4;
> }
>
> - /*
> - * 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;
> + switch (dpcd_val) {
> + default:
> + DRM_DEV_ERROR(pdata->dev,
> + "Unexpected max rate (%#x); assuming 5.4 GHz\n",
> + (int)dpcd_val);
> + /* fall through */
> case DP_LINK_BW_5_4:
> - return 7;
> + rate_valid[7] = 1;
> + /* fall through */
> + case DP_LINK_BW_2_7:
> + rate_valid[4] = 1;
> + /* fall through */
> + case DP_LINK_BW_1_62:
> + rate_valid[1] = 1;
> + break;
> }
> -
> - 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)
> @@ -609,9 +655,9 @@ static int ti_sn_link_training(struct ti_sn_bridge *pdata, int dp_rate_idx,
> static void ti_sn_bridge_enable(struct drm_bridge *bridge)
> {
> struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge);
> + bool rate_valid[ARRAY_SIZE(ti_sn_bridge_dp_rate_lut)] = { };
> const char *last_err_str = "No supported DP rate";
> int dp_rate_idx;
> - int max_dp_rate_idx;
> unsigned int val;
> int ret = -EINVAL;
>
> @@ -655,11 +701,15 @@ static void ti_sn_bridge_enable(struct drm_bridge *bridge)
> regmap_update_bits(pdata->regmap, SN_SSC_CONFIG_REG, DP_NUM_LANES_MASK,
> val);
>
> + ti_sn_bridge_read_valid_rates(pdata, rate_valid);
> +
> /* 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 < ARRAY_SIZE(ti_sn_bridge_dp_rate_lut);
> dp_rate_idx++) {
> + if (!rate_valid[dp_rate_idx])
> + continue;
> +
> ret = ti_sn_link_training(pdata, dp_rate_idx, &last_err_str);
> if (!ret)
> break;
> --
> 2.24.1.735.g03f4e72817-goog
>

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