Re: [PATCH] drm/i915: Retry on every aux read.

Jani Nikula
2015-10-20T06:58:53Z

On Tue, 20 Oct 2015, Rodrigo Vivi <rodrigo.vivi@intel.com> wrote:
> We have an inconsistency on our code on using intel_dp_dpcd_read_wake with
> retries and when using drm_dp_dpcd_read helper without retry.

We're supposed to do the retries when the sink may be in a power down
state. We're not very good at tracking that, and we've cargo culted the
retry variants all over the place without thinking. This is why we're
inconsistent.

> Since the retries help in many cases let's be consistent and be on
> the safe side retrying on every aux read, including i2c ones.

Please let's not add superfluous retries at different levels of the
stack just to be safe. It's like a variant of the C programmer's
disease.

If the retries really help [citation needed] we need to figure out what
we're doing wrong and where, and preferrably fix this at the DP helper
level for all drivers, if possible.

Other comments in-line.

>
> So we can kill the intel_dp_dpcd_read function and keep code consistent.
>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> ---
> drivers/gpu/drm/i915/intel_dp.c | 126 +++++++++++++++++-----------------------
> 1 file changed, 52 insertions(+), 74 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 09bdd94..46f3c2d 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -944,7 +944,7 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
> struct intel_dp *intel_dp = container_of(aux, struct intel_dp, aux);
> uint8_t txbuf[20], rxbuf[20];
> size_t txsize, rxsize;
> - int ret;
> + int ret, i;
>
> txbuf[0] = (msg->request << 4) |
> ((msg->address >> 16) & 0xf);
> @@ -986,17 +986,27 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
> if (WARN_ON(rxsize > 20))
> return -E2BIG;
>
> - ret = intel_dp_aux_ch(intel_dp, txbuf, txsize, rxbuf, rxsize);
> - if (ret > 0) {
> - msg->reply = rxbuf[0] >> 4;
> - /*
> - * Assume happy day, and copy the data. The caller is
> - * expected to check msg->reply before touching it.
> - *
> - * Return payload size.
> - */
> - ret--;
> - memcpy(msg->buffer, rxbuf + 1, ret);
> + /*
> + * Read with retry for link status and receiver capability reads
> + * for cases where the sink may still be asleep.
> + * Sinks are *supposed* to come up within 1ms from an off state,
> + * but we're also supposed to retry 3 times per the spec.
> + */

The comment would need an update.

> + for (i = 0, ret = 0; ret <= 0 && i < 3; i++) {
> + ret = intel_dp_aux_ch(intel_dp, txbuf, txsize,
> + rxbuf, rxsize);
> + if (ret > 0) {
> + msg->reply = rxbuf[0] >> 4;
> + /*
> + * Assume happy day, and copy the data. The caller is
> + * expected to check msg->reply before touching it.
> + *
> + * Return payload size.
> + */
> + ret--;
> + memcpy(msg->buffer, rxbuf + 1, ret);
> + } else
> + msleep(1);
> }
> break;
>
> @@ -3012,47 +3022,16 @@ static void chv_dp_post_pll_disable(struct intel_encoder *encoder)
> }
>
> /*
> - * Native read with retry for link status and receiver capability reads for
> - * cases where the sink may still be asleep.
> - *
> - * Sinks are *supposed* to come up within 1ms from an off state, but we're also
> - * supposed to retry 3 times per the spec.
> - */
> -static ssize_t
> -intel_dp_dpcd_read_wake(struct drm_dp_aux *aux, unsigned int offset,
> - void *buffer, size_t size)
> -{
> - ssize_t ret;
> - int i;
> -
> - /*
> - * Sometime we just get the same incorrect byte repeated
> - * over the entire buffer. Doing just one throw away read
> - * initially seems to "solve" it.
> - */
> - drm_dp_dpcd_read(aux, DP_DPCD_REV, buffer, 1);

See

commit f6a1906674005377b64ee5431c1418077c1b2425
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date: Thu Oct 16 20:46:09 2014 +0300

drm/i915: Do a dummy DPCD read before the actual read

> -
> - for (i = 0; i < 3; i++) {
> - ret = drm_dp_dpcd_read(aux, offset, buffer, size);
> - if (ret == size)
> - return ret;
> - msleep(1);
> - }
> -
> - return ret;
> -}
> -
> -/*
> * Fetch AUX CH registers 0x202 - 0x207 which contain
> * link status information
> */
> static bool
> intel_dp_get_link_status(struct intel_dp *intel_dp, uint8_t link_status[DP_LINK_STATUS_SIZE])
> {
> - return intel_dp_dpcd_read_wake(&intel_dp->aux,
> - DP_LANE0_1_STATUS,
> - link_status,
> - DP_LINK_STATUS_SIZE) == DP_LINK_STATUS_SIZE;
> + return drm_dp_dpcd_read(&intel_dp->aux,
> + DP_LANE0_1_STATUS,
> + link_status,
> + DP_LINK_STATUS_SIZE) == DP_LINK_STATUS_SIZE;
> }
>
> /* These are source-specific values. */
> @@ -3979,8 +3958,8 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
> struct drm_i915_private *dev_priv = dev->dev_private;
> uint8_t rev;
>
> - if (intel_dp_dpcd_read_wake(&intel_dp->aux, 0x000, intel_dp->dpcd,
> - sizeof(intel_dp->dpcd)) < 0)
> + if (drm_dp_dpcd_read(&intel_dp->aux, 0x000, intel_dp->dpcd,
> + sizeof(intel_dp->dpcd)) < 0)
> return false; /* aux transfer failed */
>
> DRM_DEBUG_KMS("DPCD: %*ph\n", (int) sizeof(intel_dp->dpcd), intel_dp->dpcd);
> @@ -3991,9 +3970,9 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
> /* Check if the panel supports PSR */
> memset(intel_dp->psr_dpcd, 0, sizeof(intel_dp->psr_dpcd));
> if (is_edp(intel_dp)) {
> - intel_dp_dpcd_read_wake(&intel_dp->aux, DP_PSR_SUPPORT,
> - intel_dp->psr_dpcd,
> - sizeof(intel_dp->psr_dpcd));
> + drm_dp_dpcd_read(&intel_dp->aux, DP_PSR_SUPPORT,
> + intel_dp->psr_dpcd,
> + sizeof(intel_dp->psr_dpcd));
> if (intel_dp->psr_dpcd[0] & DP_PSR_IS_SUPPORTED) {
> dev_priv->psr.sink_support = true;
> DRM_DEBUG_KMS("Detected EDP PSR Panel.\n");
> @@ -4004,9 +3983,9 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
> uint8_t frame_sync_cap;
>
> dev_priv->psr.sink_support = true;
> - intel_dp_dpcd_read_wake(&intel_dp->aux,
> - DP_SINK_DEVICE_AUX_FRAME_SYNC_CAP,
> - &frame_sync_cap, 1);
> + drm_dp_dpcd_readb(&intel_dp->aux,
> + DP_SINK_DEVICE_AUX_FRAME_SYNC_CAP,
> + &frame_sync_cap);
> dev_priv->psr.aux_frame_sync = frame_sync_cap ? true : false;
> /* PSR2 needs frame sync as well */
> dev_priv->psr.psr2_support = dev_priv->psr.aux_frame_sync;
> @@ -4022,15 +4001,15 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
> /* Intermediate frequency support */
> if (is_edp(intel_dp) &&
> (intel_dp->dpcd[DP_EDP_CONFIGURATION_CAP] & DP_DPCD_DISPLAY_CONTROL_CAPABLE) &&
> - (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_EDP_DPCD_REV, &rev, 1) == 1) &&
> + (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_DPCD_REV, &rev) == 1) &&
> (rev >= 0x03)) { /* eDp v1.4 or higher */
> __le16 sink_rates[DP_MAX_SUPPORTED_RATES];
> int i;
>
> - intel_dp_dpcd_read_wake(&intel_dp->aux,
> - DP_SUPPORTED_LINK_RATES,
> - sink_rates,
> - sizeof(sink_rates));
> + drm_dp_dpcd_read(&intel_dp->aux,
> + DP_SUPPORTED_LINK_RATES,
> + sink_rates,
> + sizeof(sink_rates));
>
> for (i = 0; i < ARRAY_SIZE(sink_rates); i++) {
> int val = le16_to_cpu(sink_rates[i]);
> @@ -4053,9 +4032,9 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
> if (intel_dp->dpcd[DP_DPCD_REV] == 0x10)
> return true; /* no per-port downstream info */
>
> - if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_DOWNSTREAM_PORT_0,
> - intel_dp->downstream_ports,
> - DP_MAX_DOWNSTREAM_PORTS) < 0)
> + if (drm_dp_dpcd_read(&intel_dp->aux, DP_DOWNSTREAM_PORT_0,
> + intel_dp->downstream_ports,
> + DP_MAX_DOWNSTREAM_PORTS) < 0)
> return false; /* downstream port status fetch failed */
>
> return true;
> @@ -4069,11 +4048,11 @@ intel_dp_probe_oui(struct intel_dp *intel_dp)
> if (!(intel_dp->dpcd[DP_DOWN_STREAM_PORT_COUNT] & DP_OUI_SUPPORT))
> return;
>
> - if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_SINK_OUI, buf, 3) == 3)
> + if (drm_dp_dpcd_read(&intel_dp->aux, DP_SINK_OUI, buf, 3) == 3)
> DRM_DEBUG_KMS("Sink OUI: %02hx%02hx%02hx\n",
> buf[0], buf[1], buf[2]);
>
> - if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_BRANCH_OUI, buf, 3) == 3)
> + if (drm_dp_dpcd_read(&intel_dp->aux, DP_BRANCH_OUI, buf, 3) == 3)
> DRM_DEBUG_KMS("Branch OUI: %02hx%02hx%02hx\n",
> buf[0], buf[1], buf[2]);
> }
> @@ -4089,7 +4068,7 @@ intel_dp_probe_mst(struct intel_dp *intel_dp)
> if (intel_dp->dpcd[DP_DPCD_REV] < 0x12)
> return false;
>
> - if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_MSTM_CAP, buf, 1)) {
> + if (drm_dp_dpcd_readb(&intel_dp->aux, DP_MSTM_CAP, buf)) {
> if (buf[0] & DP_MST_CAP) {
> DRM_DEBUG_KMS("Sink is MST capable\n");
> intel_dp->is_mst = true;
> @@ -4228,9 +4207,9 @@ stop:
> static bool
> intel_dp_get_sink_irq(struct intel_dp *intel_dp, u8 *sink_irq_vector)
> {
> - return intel_dp_dpcd_read_wake(&intel_dp->aux,
> - DP_DEVICE_SERVICE_IRQ_VECTOR,
> - sink_irq_vector, 1) == 1;
> + return drm_dp_dpcd_readb(&intel_dp->aux,
> + DP_DEVICE_SERVICE_IRQ_VECTOR,
> + sink_irq_vector) == 1;
> }
>
> static bool
> @@ -4238,9 +4217,9 @@ intel_dp_get_sink_irq_esi(struct intel_dp *intel_dp, u8 *sink_irq_vector)
> {
> int ret;
>
> - ret = intel_dp_dpcd_read_wake(&intel_dp->aux,
> - DP_SINK_COUNT_ESI,
> - sink_irq_vector, 14);
> + ret = drm_dp_dpcd_read(&intel_dp->aux,
> + DP_SINK_COUNT_ESI,
> + sink_irq_vector, 14);
> if (ret != 14)
> return false;
>
> @@ -4496,8 +4475,7 @@ intel_dp_detect_dpcd(struct intel_dp *intel_dp)
> intel_dp->downstream_ports[0] & DP_DS_PORT_HPD) {
> uint8_t reg;
>
> - if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_SINK_COUNT,
> - &reg, 1) < 0)
> + if (drm_dp_dpcd_readb(&intel_dp->aux, DP_SINK_COUNT, &reg) < 0)
> return connector_status_unknown;
>
> return DP_GET_SINK_COUNT(reg) ? connector_status_connected
> --
> 2.4.3
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

--
Jani Nikula, Intel Open Source Technology Center