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Thu, 16 Jul 2026 17:07:10 +0200 (CEST) Message-ID: <7753ee98-a8c6-4535-8789-d915b0f79ddf@collabora.com> Date: Thu, 16 Jul 2026 18:07:09 +0300 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 04/39] drm/connector: Add HDMI 2.0 scrambler infrastructure To: Maxime Ripard Cc: Dmitry Baryshkov , Maarten Lankhorst , Thomas Zimmermann , David Airlie , Simona Vetter , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Luca Ceresoli , Sandy Huang , =?UTF-8?Q?Heiko_St=C3=BCbner?= , Andy Yan , Daniel Stone , Dave Stevenson , =?UTF-8?Q?Ma=C3=ADra_Canal?= , Raspberry Pi Kernel Maintenance , kernel@collabora.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org References: <20260702-dw-hdmi-qp-scramb-v8-0-d79890d00b6a@collabora.com> <20260702-dw-hdmi-qp-scramb-v8-4-d79890d00b6a@collabora.com> <17753a1c-824a-4835-ac2d-8b2796bba1eb@collabora.com> <534b921c-638c-4fc3-b89e-5dfc1f269f96@collabora.com> <20260713-statuesque-nonchalant-seagull-b9c39d@houat> <91c3a825-3344-4ff5-8ea0-f8f057665b3f@collabora.com> <20260715-ancient-zealous-eagle-b13e94@houat> <20260716-astute-nippy-moose-bd22b5@houat> Content-Language: en-US From: Cristian Ciocaltea In-Reply-To: <20260716-astute-nippy-moose-bd22b5@houat> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260716_080714_369830_7D0D18DF X-CRM114-Status: GOOD ( 26.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 7/16/26 4:50 PM, Maxime Ripard wrote: > On Wed, Jul 15, 2026 at 01:46:12PM +0300, Cristian Ciocaltea wrote: >> On 7/15/26 11:55 AM, Maxime Ripard wrote: >>> On Mon, Jul 13, 2026 at 01:23:00PM +0300, Cristian Ciocaltea wrote: >>>> On 7/13/26 11:50 AM, Maxime Ripard wrote: >>>>> On Thu, Jul 09, 2026 at 10:25:54PM +0300, Cristian Ciocaltea wrote: >>>>>> On 7/3/26 11:54 PM, Cristian Ciocaltea wrote: >>>>>>> On 7/3/26 5:34 PM, Dmitry Baryshkov wrote: >>>>>>>> On Thu, Jul 02, 2026 at 05:46:17PM +0300, Cristian Ciocaltea wrote: >>>>>>>>> Add the connector-level infrastructure to support HDMI 2.0 scrambling: >>>>>>>>> >>>>>>>>> - A scrambler_supported flag to indicate whether the source supports the >>>>>>>>> scrambling capability, in which case the newly introduced >>>>>>>>> .scrambler_{enable|disable}() callbacks in drm_connector_hdmi_funcs >>>>>>>>> are mandatory >>>>>>>> >>>>>>>> Do we need a flag? What would it mean if the flag is set, but the >>>>>>>> callbacks are not? Can we drop the flag and use the presence of the >>>>>>>> callbacks as a way to identify that scrambler is enabled? >>>>>>> >>>>>>> The flag is intended to be set only within drmm_connector_hdmi_init_with_caps() >>>>>>> when drivers advertise HDMI 2.x capability, in which case it also ensures the >>>>>>> callbacks are provided. >>>>>>> >>>>>>> We could drop the flag and instead have the init helper clear the callbacks if >>>>>>> they were provided for HDMI 1.x. This might slightly reduce code readability, >>>>>>> as it relies on checking the presence of individual callbacks - especially since >>>>>>> we plan to extend this further with HDMI 2.1 support, providing four or five >>>>>>> additional FRL-specific callbacks. >>>>>> >>>>>> I tried to replace the flag with a helper that checks the presence of (one of) >>>>>> the callbacks, but it's not straightforward to unset those for non-HDMI 2.x >>>>>> cases since the hdmi_funcs argument is immutable. >>>>> >>>>> I'm not sure why we would need to unset them. If the driver states that >>>>> it support HDMI 2.0, then it needs to be there, if it doesn't, then who >>>>> cares? it's not going to be used. We can log a warning that it's >>>>> inconsistent I guess, but there's no need to actively remove it. >>>> >>>> I was trying to address the use case where drivers provide the scrambler >>>> callbacks despite not supporting HDMI 2.0. >>> >>> Scrambling got introduced with HDMI 2.0. That doesn't make sense, but >>> it's not a total deal breaker, it's just going to be here unused. Hence >>> why I was suggesting to put a warning there if you wanted to. >>> >>>> If we replace the scrambler_supported flag with a helper checking the >>>> presence of the scrambler callbacks, then we would need to ensure the >>>> callbacks do not exist in this case. >>> >>> Keep it simple: >>> >>> if (hdmi_version >= HDMI_VERSION_2_0) >>> if (funcs->scrambler_enable) >>> hdmi->scramblers_supported = true >>> else >>> return -EINVAL >>> else >>> drm_warn(warn, "Inconsistent HDMI version"); >>> >>> We don't need anything more than that. >> >> I dropped the scrambler_supported flag and introduced a helper: >> >> static inline bool >> drm_connector_hdmi_scrambler_supported(struct drm_connector *connector) >> { >> return connector->hdmi.funcs && connector->hdmi.funcs->scrambler_enable; > > I'd add disable to that test If scrambler_enable is present, scrambler_disable is also present, as guaranteed by the init validation below. I assume you'd like to have it added regardless, to improve code readability, which is a fair point. >> } >> >> Therefore we need to ensure the callbacks are not set in the HDMI 1.x cases: >> >> int drmm_connector_hdmi_init_with_caps() >> { >> ... >> if (caps->supported_hdmi_ver >= HDMI_VERSION_2_0) { >> if (!hdmi_funcs->scrambler_enable || >> !hdmi_funcs->scrambler_disable) >> return -EINVAL; >> >> connector->hdmi.max_tmds_char_rate = HDMI_2_0_TMDS_CHAR_RATE_MAX_HZ; >> } else { >> /* >> * Scrambler callbacks are only valid for connectors advertising >> * HDMI 2.0 capability. drm_connector_hdmi_scrambler_supported() >> * relies on their presence to report scrambling support. >> */ >> if (hdmi_funcs->scrambler_enable || >> hdmi_funcs->scrambler_disable) >> return -EINVAL; >> >> if (caps->supported_hdmi_ver >= HDMI_VERSION_1_3) { >> connector->hdmi.max_tmds_char_rate = HDMI_1_3_TMDS_CHAR_RATE_MAX_HZ; >> } else if (caps->supported_hdmi_ver >= HDMI_VERSION_1_0) { >> connector->hdmi.max_tmds_char_rate = HDMI_1_0_TMDS_CHAR_RATE_MAX_HZ; >> } >> } > > Drivers might have a lower limit than the max allowed by the spec. It > should be provided by the driver, possibly optionally with a fallback to > what the spec states? Yes, this has been already part of patch 2 (also added an error message to help with debugging): if (caps->max_tmds_char_rate) { if (caps->max_tmds_char_rate > connector->hdmi.max_tmds_char_rate) { drm_err(dev, "Enforced max_tmds_char_rate exceeds %llu spec limit\n", connector->hdmi.max_tmds_char_rate); return -EINVAL; } connector->hdmi.max_tmds_char_rate = caps->max_tmds_char_rate; } Regards, Cristian