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Message-ID: <8735z5t5qz.fsf@intel.com>
Date: Wed, 13 Jan 2021 13:51:00 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Koba Ko <koba.ko@...onical.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>, Lyude Paul <lyude@...hat.com>,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/dp_mst: Align mst link rate with soure rate
On Wed, 13 Jan 2021, Koba Ko <koba.ko@...onical.com> wrote:
> After read the link rate from MST hub, align with
> maximum source rate.
>
> Signed-off-by: Koba Ko <koba.ko@...onical.com>
> ---
> drivers/gpu/drm/drm_dp_mst_topology.c | 8 ++++++++
> drivers/gpu/drm/i915/display/intel_dp.c | 7 +++++++
> include/drm/drm_dp_helper.h | 8 ++++++++
> include/drm/drm_dp_mst_helper.h | 4 ++++
> 4 files changed, 27 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 6982ecbf30b5..e7ceae97be85 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3672,6 +3672,10 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
> {
> int ret = 0;
> struct drm_dp_mst_branch *mstb = NULL;
> + unsigned int max_link_rate_tbl[MAX_DRM_DP_MAX_RATE + 1] = {
> + DP_LINK_BW_1_62, DP_LINK_BW_2_7, DP_LINK_BW_5_4,
> + DP_LINK_BW_8_1, DP_LINK_RATE_TABLE
> + };
Please no. Read on for why.
>
> mutex_lock(&mgr->payload_lock);
> mutex_lock(&mgr->lock);
> @@ -3693,6 +3697,9 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
> goto out_unlock;
> }
>
> + if (mgr->max_source_rate < MAX_DRM_DP_MAX_RATE)
> + mgr->dpcd[1] = max_link_rate_tbl[mgr->max_source_rate];
Make ->max_source_rate the actual physical rate in kHz, and use
drm_dp_link_rate_to_bw_code() here.
> +
> mgr->pbn_div = drm_dp_get_vc_payload_bw(mgr->dpcd[1],
> mgr->dpcd[2] & DP_MAX_LANE_COUNT_MASK);
> if (mgr->pbn_div == 0) {
> @@ -5422,6 +5429,7 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
> mgr->aux = aux;
> mgr->max_dpcd_transaction_bytes = max_dpcd_transaction_bytes;
> mgr->max_payloads = max_payloads;
> + mgr->max_source_rate = MAX_DRM_DP_MAX_RATE;
> mgr->conn_base_id = conn_base_id;
> if (max_payloads + 1 > sizeof(mgr->payload_mask) * 8 ||
> max_payloads + 1 > sizeof(mgr->vcpi_mask) * 8)
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 469e765a1b7b..a89b4c823123 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5392,6 +5392,13 @@ intel_dp_configure_mst(struct intel_dp *intel_dp)
> intel_dp->is_mst = sink_can_mst &&
> i915->params.enable_dp_mst;
>
> + if (intel_dp_source_supports_hbr3(intel_dp))
> + intel_dp->mst_mgr.max_source_rate = DRM_DP_MAX_RATE_HBR3;
> + else if (intel_dp_source_supports_hbr2(intel_dp))
> + intel_dp->mst_mgr.max_source_rate = DRM_DP_MAX_RATE_HBR2;
> + else
> + intel_dp->mst_mgr.max_source_rate = DRM_DP_MAX_RATE_HBR;
Whenever this file references a "rate", it's the rate in kHz. This is
confusing. Use the rate in kHz.
Also, please look at how intel_dp_source_supports_hbr* are implemented;
we already have all the supported source rates cached in intel_dp.
The max source rate is:
intel_dp->source_rates[intel_dp->num_source_rates - 1].
No need to do the if ladder here at all. If you like, you can add a
helper:
int intel_dp_max_source_rate(struct intel_dp *intel_dp)
{
return intel_dp->source_rates[intel_dp->num_source_rates - 1];
}
and reuse that in the supports_hbr* functions:
bool intel_dp_source_supports_hbr2(struct intel_dp *intel_dp)
{
return intel_dp_max_source_rate(intel_dp) >= 540000;
}
> +
> drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr,
> intel_dp->is_mst);
> }
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 6236f212da61..ef2b328469cd 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -183,6 +183,14 @@ struct drm_device;
> #define DP_SUPPORTED_LINK_RATES 0x010 /* eDP 1.4 */
> # define DP_MAX_SUPPORTED_RATES 8 /* 16-bit little-endian */
>
> +enum drm_dp_max_link_rate {
> + DRM_DP_MAX_RATE_RBR = 0,
> + DRM_DP_MAX_RATE_HBR,
> + DRM_DP_MAX_RATE_HBR2,
> + DRM_DP_MAX_RATE_HBR3,
> + MAX_DRM_DP_MAX_RATE
> +};
We already have 1) actual physical rates, in kHz, and 2) the DPCD rate
codes, such as DP_LINK_BW_1_62.
Do *not* add a third representation. Prefer kHz throughout, and convert
to/from the DPCD codes near where they are needed.
> +
> /* Multiple stream transport */
> #define DP_FAUX_CAP 0x020 /* 1.2 */
> # define DP_FAUX_CAP_1 (1 << 0)
> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> index f5e92fe9151c..e7d8c899fea0 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -593,6 +593,10 @@ struct drm_dp_mst_topology_mgr {
> * @max_payloads: maximum number of payloads the GPU can generate.
> */
> int max_payloads;
> + /**
> + * @max_source_rate: maximum link rate of source.
> + */
> + int max_source_rate;
Again, make this the actual rate in kHz. That's what I'd think it is by
reading the comment above anyway.
> /**
> * @conn_base_id: DRM connector ID this mgr is connected to. Only used
> * to build the MST connector path value.
--
Jani Nikula, Intel Open Source Graphics Center
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