Re: [PATCH 7/8] drm/i915: Fix random aux transactions failures.

Jani Nikula
2015-11-23T10:10:32Z

I don't see how the subject matches the commit.

On Sat, 21 Nov 2015, Rodrigo Vivi <rodrigo.vivi@intel.com> wrote:
> This read wake with retries were initially added by 2 commits:
>
> commit 61da5fab ("drm/i915/dp: retry link status read 3 times on failure")
> commit 899526d9 ("drm/i915/dp: try to read receiver capabilities 3 times when detecting")
>
> Both mentioning section 9.1 of the 1.1a DisplayPort spec, that actually
> tell us to retry three times on certain case when "writing 01h to DPCD address 600h"
> and this code is already in place in our driver. Added by:
>
> commit c7ad3810 ("drm/i915/dp: manage sink power state if possible")

I still think what we currently do for the sink power state management
works by coincidence. We should still look into it.

However, I think this series overall (apart from patch 6/8 which really
is a bummer, the comment inline below, and the minor other comments)
looks like worthwhile changes. We can leave the power state management
for later. Or rip it out for now...

> At this point we have no visibility if those patches were added to workaround certain
> corner cases like lazy dongles or what, but also at that time there wasn't enough
> retries on the proper places.
>
> So my proposal is to remove these retries for now that we have drm handling the retries
> and if we face any corner case back again we study it to return EAGAIN or EBUSY
> to force retries at drm instead of handling them here.
>
> v2: Improve commit message trying to explain the origin of the retries.
>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> ---
> drivers/gpu/drm/i915/intel_dp.c | 95 ++++++++++++++---------------------------
> 1 file changed, 32 insertions(+), 63 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index c87e937..2ce6527 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -985,7 +985,8 @@ 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);
> + ret = intel_dp_aux_ch(intel_dp, txbuf, txsize,
> + rxbuf, rxsize);
> if (ret > 0) {
> msg->reply = rxbuf[0] >> 4;
> /*
> @@ -3150,47 +3151,16 @@ 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);

This still needs to be addressed somehow. Maybe it's sufficient for
Ville to test with his monitor?

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
> */
> 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. */
> @@ -3825,8 +3795,8 @@ 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);
> @@ -3837,9 +3807,9 @@ 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");
> @@ -3850,9 +3820,9 @@ 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;
> @@ -3868,15 +3838,15 @@ 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]);
> @@ -3899,9 +3869,9 @@ 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;
> @@ -3915,11 +3885,11 @@ 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]);
> }
> @@ -3935,7 +3905,7 @@ 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;
> @@ -4072,9 +4042,9 @@ 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
> @@ -4082,9 +4052,9 @@ 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;
>
> @@ -4343,8 +4313,7 @@ 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

--
Jani Nikula, Intel Open Source Technology Center