From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout-p-103.mailbox.org (mout-p-103.mailbox.org [80.241.56.161]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BE36A1A6830 for ; Tue, 24 Mar 2026 16:44:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=80.241.56.161 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774370680; cv=none; b=jn6AdCLjWNmAz9NfDS/8lcj9BMhq/5kQYG7r1rXTBL/L2BNFHu2BMsHpNSkd5ZMQCxphgZgijMJRSSWMKlMn1z2XE9doWxN2YRTlJswUr8sypVUx6AQByjw9NBRehR+ofoSEm/4KAe2sLIcw0ZMwQqrOxORXfy4DVCm+lLn+42w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774370680; c=relaxed/simple; bh=pI1bWafIdd5BkRABvxEGZ8n+x+zmz7O3Zn3nUuudeiA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AYcH6bVKnCG5P2YxKOPei9aML/jfDUIUeg4rvp1OvJMt+4K4Ep/lBvA+cfoGsHl1vsEL/uyBZGk2UK+tDYyEef6FdfQDF5JtQ7S3UXapPQ3Xio6iCUKPAgiCjPC5Y7+Z7u8rVgtofphVqI+k3XVCRRAvHRh78qHXHgAIxlKpT40= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mailbox.org; spf=pass smtp.mailfrom=mailbox.org; dkim=pass (2048-bit key) header.d=mailbox.org header.i=@mailbox.org header.b=CBlDSMBZ; arc=none smtp.client-ip=80.241.56.161 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mailbox.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mailbox.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=mailbox.org header.i=@mailbox.org header.b="CBlDSMBZ" Received: from smtp2.mailbox.org (smtp2.mailbox.org [IPv6:2001:67c:2050:b231:465::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-103.mailbox.org (Postfix) with ESMTPS id 4fgG8r3SHWz9v1Q; Tue, 24 Mar 2026 17:44:28 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mailbox.org; s=mail20150812; t=1774370668; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=i6jFxC5QqAnVKARAaOlj7wQMriWLDHrAHv85BO6JVIc=; b=CBlDSMBZegpzqYTMaWbIexH5fv/MSRWqzFrZW1yA9LOsuKvtKAWs/KNcLs/34zgvyXF2zm CyGm73lJZ11VATDG38CO+1aBmNBnwaoeAAtpDQ/uWg0OXctLHQI2U4TJmsibPfHZm/DL7P Ism+wCTLmg2ph/WGSy7YqUEWSOKDdyOWX4JnURLP0oj91R9OTtJzANHkUjl4wnUlCkjLDN 6HjTNmhnTyzMR9f1Y8zo1k7fBgrzC77jbzikhj0FpCzH/GFpCuzur4/y8eS7ZkT5CEPwXk y2ThqvxW0eG5HkHCepOgxIkoBGqmh7QazzElTAvo0a7ZQTSiIzOiHr/8HEpwLw== Message-ID: <254c20a4-cce3-4c8e-9902-514586f3e694@mailbox.org> Date: Tue, 24 Mar 2026 17:44:21 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v5 0/3] Add "link bpc" DRM property To: Nicolas Frattaroli , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Harry Wentland , Leo Li , Rodrigo Siqueira , Alex Deucher , =?UTF-8?Q?Christian_K=C3=B6nig?= , =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= , Daniel Stone , Dmitry Baryshkov Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, kernel@collabora.com, Derek Foreman , Marius Vlad References: <20260319-link-bpc-v5-0-5306cd04a708@collabora.com> <8676926.T7Z3S40VBb@workhorse> <4265353.aeNJFYEL58@workhorse> From: =?UTF-8?Q?Michel_D=C3=A4nzer?= Content-Language: en-CA In-Reply-To: <4265353.aeNJFYEL58@workhorse> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-MBO-RS-ID: 8579321637022c6ad0a X-MBO-RS-META: enrgji945et541zmwxco1a6gnwnhtgbb On 3/24/26 16:25, Nicolas Frattaroli wrote: > On Monday, 23 March 2026 18:27:41 Central European Standard Time Michel Dänzer wrote: >> On 3/23/26 17:55, Nicolas Frattaroli wrote: >>> >>> "Someone might not understand its purpose" is, in my eyes, not a valid reason to >>> not have this property, [...] >> Per my previous posts, that's not my concern. > > Then what is your concern? Per my previous posts, my concerns are: * The meaning of the "link bpc" property value isn't defined well enough vs things like dithering or DSC, which will likely result in compositors / users overestimating what value they need / want, resulting in compositors spuriously rejecting configurations which would work perfectly fine, and/or spurious issue reports. With my compositor developer hat on, what I'd want to know is something like: "How many bits of information can be passed over the link, allowing the display to present it in a way which can be perceived by the user?" With dithering or DSC, that would be a higher value than the physical link bpc. * There's no clear use case. This is generally a requirement for new KMS UAPI. The practical usefulness of the corresponding weston MR is dubious per the concern above. > That the link-bpc property does not consider DSC and dithering? > Two things which the max-bpc property also does not consider? It's not (as much of) an issue with the "max bpc" property because it's just an upper limit, the driver is free to use a lower effective bpc. > If all you want is a clearer description of the property in the comment that > accompanies it, then I can do that, and I said I agree with this point. Patch 3 would need to take dithering & DSC into account as well. > But you seem to be arguing from a position of not wanting the property to > exist at all, [...] I'm not. However, per the first concern above, a not-well-defined property could be worse than none. -- Earthling Michel Dänzer \ GNOME / Xwayland / Mesa developer https://redhat.com \ Libre software enthusiast