From: Manasi Navare <manasi.d.navare@intel.com>
To: Damian Kos <dkos@cadence.com>
Cc: "David Airlie" <airlied@linux.ie>,
"Rob Herring" <robh+dt@kernel.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"Archit Taneja" <architt@codeaurora.org>,
"Andrzej Hajda" <a.hajda@samsung.com>,
"Laurent Pinchart" <Laurent.pinchart@ideasonboard.com>,
"Gustavo Padovan" <gustavo@padovan.org>,
"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
"Sean Paul" <sean@poorly.run>, "Sandy Huang" <hjc@rock-chips.com>,
"Heiko Stübner" <heiko@sntech.de>,
dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-rockchip@lists.infradead.org, quentin.schulz@bootlin.com,
jartur@cadence.com, jbergsagel@ti.com, ltyrala@cadence.com,
stelford@cadence.com,
"Quentin Schulz" <quentin.schulz@free-electrons.com>,
pgaj@cadence.com, piotrs@cadence.com
Subject: Re: [PATCH v4 2/5] drm/dp: fix link probing for devices supporting DP 1.4+
Date: Fri, 21 Sep 2018 00:59:30 -0700 [thread overview]
Message-ID: <20180921075929.GA28323@intel.com> (raw)
In-Reply-To: <1537455288-20223-3-git-send-email-dkos@cadence.com>
Thanks for the patch. Verified with the DP 1.4 spec and looks good to me.
Also look at the related patch that makes use of the correct extended capabilities:
https://patchwork.freedesktop.org/patch/249400/
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Manasi
On Thu, Sep 20, 2018 at 03:54:37PM +0100, Damian Kos wrote:
> From: Quentin Schulz <quentin.schulz@free-electrons.com>
>
> DP 1.4 introduced a DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit in
> DP_TRAINING_AUX_RD_INTERVAL register. If set, DPCD registers from
> DP_DPCD_REV to DP_ADAPTER_CAP should be retrieved starting from
> DP_DPCD_REV_EXTENDED. All registers are copied except DP_DPCD_REV,
> DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT which represent the
> "true capabilities" of DPRX device.
>
> Original DP_DPCD_REV, DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT
> might falsely return lower capabilities to "avoid interoperability
> issues with some of the existing DP Source devices that malfunction
> when they discover the higher capabilities within those three
> registers.".
>
> Before DP 1.4, DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit was reserved
> and read 0 so it's safe to check against it even if DP revision is
> <1.4
>
> Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
> Signed-off-by: Damian Kos <dkos@cadence.com>
> ---
> drivers/gpu/drm/drm_dp_helper.c | 30 +++++++++++++++++++++++++++++-
> 1 file changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 8c6b9fd89f8a..735ebde5c2f0 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -370,10 +370,38 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
> {
> u8 values[3];
> int err;
> + unsigned int addr;
>
> memset(link, 0, sizeof(*link));
>
> - err = drm_dp_dpcd_read(aux, DP_DPCD_REV, values, sizeof(values));
> + /*
> + * DP 1.4 introduced a DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit in
> + * DP_TRAINING_AUX_RD_INTERVAL register. If set, DPCD registers from
> + * DP_DPCD_REV to DP_ADAPTER_CAP should be retrieved starting from
> + * DP_DPCD_REV_EXTENDED. All registers are copied except DP_DPCD_REV,
> + * DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT which represent the
> + * "true capabilities" of DPRX device.
> + *
> + * Original DP_DPCD_REV, DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT
> + * might falsely return lower capabilities to "avoid interoperability
> + * issues with some of the existing DP Source devices that malfunction
> + * when they discover the higher capabilities within those three
> + * registers.".
> + *
> + * Before DP 1.4, DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit was reserved
> + * and read 0 so it's safe to check against it even if DP revision is
> + * <1.4
> + */
> + err = drm_dp_dpcd_readb(aux, DP_TRAINING_AUX_RD_INTERVAL, values);
> + if (err < 0)
> + return err;
> +
> + if (values[0] & DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT)
> + addr = DP_DP13_DPCD_REV;
> + else
> + addr = DP_DPCD_REV;
> +
> + err = drm_dp_dpcd_read(aux, addr, values, sizeof(values));
> if (err < 0)
> return err;
>
> --
> 2.17.1
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
next prev parent reply other threads:[~2018-09-21 7:57 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-20 14:54 [PATCH v4 0/5] drm: add support for Cadence MHDP DPI/DP bridge Damian Kos
2018-09-20 14:54 ` [PATCH v4 1/5] drm/rockchip: prepare common code for cdns and rk dpi/dp driver Damian Kos
2018-09-20 14:54 ` [PATCH v4 2/5] drm/dp: fix link probing for devices supporting DP 1.4+ Damian Kos
2018-09-21 7:59 ` Manasi Navare [this message]
2018-10-01 9:27 ` Quentin Schulz
2018-10-02 13:28 ` Ville Syrjälä
2018-09-20 14:54 ` [PATCH v4 3/5] drm/dp: make dp_get_lane_status usable from outside of the core Damian Kos
2018-09-20 14:54 ` [PATCH v4 4/5] dt-bindings: drm/bridge: Document Cadence MHDP bridge bindings Damian Kos
2018-09-20 14:54 ` [PATCH v4 5/5] drm: bridge: add support for Cadence MHDP DPI/DP bridge Damian Kos
2018-09-21 8:41 ` Heiko Stuebner
2018-09-24 11:40 ` Damian Kos
2018-09-24 12:28 ` Heiko Stuebner
2018-09-24 12:47 ` Damian Kos
2018-09-21 14:01 ` Sean Paul
2018-09-24 10:22 ` Damian Kos
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