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h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=Cmp1zkJeb75hdD0GB2WOsrT3TzHWyFI65GOyYes9D0MDgCSGmnXg491UhlnZuXe8P X1limW0xZudgcxX0gCcfi0iRkDl9yA4RiaVBYrrK2ZHYgPRHsZ85NaeDioQ9T6PC1H GmtkrNOXVV2HY24VnRtMQAo8seUvBTqYV+0pBx66zKuFFq4med9bK8njFCMpFItMJz AzcnuAshyvrgSgEsbIJWeCuVeQmMzu6ibF8i0WWp9Uw5VLU+z4ywF6NfX9kKAUIXH8 SIVPO9//8AkJSWTz6OUvddWZXDSEKLpxm06R5Ir55hnxAZ9Ausq6TXyV9j3l14LT+o h9fVekEGF8r3Q== Received: from localhost (unknown [100.64.0.241]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange secp256r1 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: cristicc) by bali.collaboradmins.com (Postfix) with ESMTPSA id 3440717E090B; Fri, 31 Jul 2026 18:19:21 +0200 (CEST) From: Cristian Ciocaltea Date: Fri, 31 Jul 2026 19:19:16 +0300 Subject: [PATCH v10 09/69] drm/display: scdc-helper: Add helper to set SCDC version information Precedence: bulk X-Mailing-List: linux-sunxi@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20260731-dw-hdmi-qp-scramb-v10-9-294364b2cf15@collabora.com> References: <20260731-dw-hdmi-qp-scramb-v10-0-294364b2cf15@collabora.com> In-Reply-To: <20260731-dw-hdmi-qp-scramb-v10-0-294364b2cf15@collabora.com> To: Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Luca Ceresoli , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Chen-Yu Tsai , Samuel Holland , Dave Stevenson , =?utf-8?q?Ma=C3=ADra_Canal?= , Raspberry Pi Kernel Maintenance , Sandy Huang , =?utf-8?q?Heiko_St=C3=BCbner?= , Andy Yan , Algea Cao , Daniel Stone , Liu Ying , Phong LE Cc: kernel@collabora.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev, linux-rockchip@lists.infradead.org, Dmitry Baryshkov , Maud Spierings , Diederik de Haas X-Mailer: b4 0.15.2 X-MORS-Enabled: yes X-MORS-DOMAIN: patchwork.local X-MORS-HOSTING: hosting172546 X-MORS-USER: hosting172546 X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= The HDMI 2.x specs mandate that compliant Sink devices report their SCDC version in the Sink Version register, which reads as 1 on any SCDC-capable sink. There is also a dedicated Source Version register. Writing it is not compulsory, but the spec advises that compliant Source devices do so, in which case the value must be 1. Add drm_scdc_set_source_version() to follow this recommendation. The Sink Version register is read first, both to log the advertised SCDC version and to guard against non-conformant devices: a sink reporting version 0 is either not SCDC-version-aware or broken, so writing the source version gains nothing and risks upsetting such hardware. In that case the write is skipped. The source version is passed as a parameter rather than hardcoded, as future spec revisions may define additional rules for the allowable version values. The written value is additionally clamped to the sink's reported version so the source never advertises a version the sink does not understand. Acked-by: Maxime Ripard Reviewed-by: Dmitry Baryshkov Tested-by: Maud Spierings Tested-by: Diederik de Haas # NanoPC-T6 LTS, Rock 5B Signed-off-by: Cristian Ciocaltea --- drivers/gpu/drm/display/drm_scdc_helper.c | 46 ++++++++++++++++++++++++++++++- include/drm/display/drm_scdc_helper.h | 2 ++ 2 files changed, 47 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/display/drm_scdc_helper.c b/drivers/gpu/drm/display/drm_scdc_helper.c index cb6632346aad..6d804ee19420 100644 --- a/drivers/gpu/drm/display/drm_scdc_helper.c +++ b/drivers/gpu/drm/display/drm_scdc_helper.c @@ -21,10 +21,11 @@ * DEALINGS IN THE SOFTWARE. */ +#include #include #include +#include #include -#include #include #include @@ -270,3 +271,46 @@ bool drm_scdc_set_high_tmds_clock_ratio(struct drm_connector *connector, return true; } EXPORT_SYMBOL(drm_scdc_set_high_tmds_clock_ratio); + +/** + * drm_scdc_set_source_version - set SCDC source version on the sink + * @connector: connector + * @ver: source version to advertise (per spec, 1) + * + * Reads the sink version for diagnostics and as a guard, then writes + * the source version unless the sink reports version 0. + * + * Returns: + * 0 on success or when skipped; a negative error code when either + * the read or the write failed. + */ +int drm_scdc_set_source_version(struct drm_connector *connector, u8 ver) +{ + u8 sink_ver; + int ret; + + ret = drm_scdc_readb(connector->ddc, SCDC_SINK_VERSION, &sink_ver); + if (ret) { + drm_scdc_dbg(connector, "Failed to read SCDC_SINK_VERSION: %d\n", ret); + return ret; + } + + drm_scdc_dbg(connector, "Sink reported SCDC ver. %u\n", sink_ver); + + /* + * Only advertise our source version to sinks that report a + * non-zero sink version. A sink reporting version 0 is either + * not SCDC-version-aware or non-conformant; writing the source + * version gains nothing and may upset broken hardware. + */ + if (sink_ver) { + ret = drm_scdc_writeb(connector->ddc, SCDC_SOURCE_VERSION, + min_t(u8, sink_ver, ver)); + if (ret) + drm_scdc_dbg(connector, + "Failed to write SCDC_SOURCE_VERSION: %d\n", ret); + } + + return ret; +} +EXPORT_SYMBOL(drm_scdc_set_source_version); diff --git a/include/drm/display/drm_scdc_helper.h b/include/drm/display/drm_scdc_helper.h index 34600476a1b9..90b0828364c2 100644 --- a/include/drm/display/drm_scdc_helper.h +++ b/include/drm/display/drm_scdc_helper.h @@ -77,4 +77,6 @@ bool drm_scdc_get_scrambling_status(struct drm_connector *connector); bool drm_scdc_set_scrambling(struct drm_connector *connector, bool enable); bool drm_scdc_set_high_tmds_clock_ratio(struct drm_connector *connector, bool set); +int drm_scdc_set_source_version(struct drm_connector *connector, u8 ver); + #endif