From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) (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 719AA3ED5B3 for ; Wed, 15 Jul 2026 10:34:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.251.105.195 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784111663; cv=none; b=kNHsjJlEpfwq3X1pEqVh03TnLAz27363ri2kVhTATGOXNIux8z4IDMrHSc222hkREh4X7HZYOn23L3l64J7PEutB8l+/szktoFt6qc9YwvKG1hdGdV9zEdbBByr5Je2UNJtupvubLKcF5Ji8/3spqpokciLxvs+xkYNPnvZ6Quw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784111663; c=relaxed/simple; bh=IkJnX4Q0f685MGMac/EYnUgIc/6fHPJFWwoic2nfCBc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pfdSys2OQbBDd/uXYj9Sv+D1PYRvE9lCmb7vb6mnymeohJxEG+qMBsTgwHUaL+mlUrcaDBBj0c35JNUj4+A1xHjK5EjgbWZAiRLScZ/L9bK5ij3fWpddz2bvKEn+MuiBoFQE5iU8vq6xICsjntBgJwY9ESlG+g1RoC15S72JPdY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=CxCfyxWQ; arc=none smtp.client-ip=148.251.105.195 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="CxCfyxWQ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1784111660; bh=IkJnX4Q0f685MGMac/EYnUgIc/6fHPJFWwoic2nfCBc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=CxCfyxWQoK2fMzcMWdxysiIbfEO8pWawDkEtOLsZZ0z/6FsDYUX9OULxrqC34oZBH N68/5SZtUEdYAw4scbkcZjpFg/Id+Eby8XuPmPeFHpm/q3EJX+NbmL0H1pjqvmWRw2 gf/OEkv50g2ICcYVGLdLUgXivS9ZmP2fSOAxiHnTSWtIZyI4LK0n/p8oHW1qk3223k SRVRWYRp3xksrLBDUA/s2i7yxt8IetEFDamBHOYIJdxDpqlXBfdfDAKx4HrQ79DXi2 W34Lpeah3JDsmGJLzVLIx1MxfDGrHbcBiVl8234GCfyq2FhRBGRDObQEGoUqUb2s9/ JfJBXjRblX3zg== Received: from [100.64.0.241] (unknown [100.64.0.241]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange x25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: cristicc) by bali.collaboradmins.com (Postfix) with ESMTPSA id BAB4A17E0076; Wed, 15 Jul 2026 12:34:19 +0200 (CEST) Message-ID: <45113534-94ad-4a0f-8014-c04e9ab67a26@collabora.com> Date: Wed, 15 Jul 2026 13:34:19 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 02/39] drm/connector: Add caps-based HDMI connector init helper 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-v8-2-d79890d00b6a@collabora.com> <20260707-illegal-tuna-of-force-1c06e3@houat> <737678ab-f082-4a0e-b453-f403ba141437@collabora.com> <80374deb-3246-413f-a043-66bcdb438ab1@collabora.com> <20260715-fair-opalescent-rhino-c6407b@houat> Content-Language: en-US From: Cristian Ciocaltea In-Reply-To: <20260715-fair-opalescent-rhino-c6407b@houat> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/15/26 11:50 AM, Maxime Ripard wrote: > On Fri, Jul 10, 2026 at 01:27:37PM +0300, Cristian Ciocaltea wrote: >> On 7/8/26 1:11 PM, Cristian Ciocaltea wrote: >>> Hi Maxime, >>> >>> On 7/7/26 7:10 PM, Maxime Ripard wrote: >>>> On Fri, Jul 03, 2026 at 10:31:55PM +0300, Cristian Ciocaltea wrote: >>>>> Hi Dmitry, >>>>> >>>>> Thanks for your quick review! >>>>> >>>>> On 7/3/26 5:05 PM, Dmitry Baryshkov wrote: >>>>>> On Thu, Jul 02, 2026 at 05:46:15PM +0300, Cristian Ciocaltea wrote: >>>>>>> In preparation for adding HDMI 2.x source capabilities, introduce struct >>>>>>> drm_connector_hdmi_caps and a new drmm_connector_hdmi_init_with_caps() >>>>>>> helper. >>>>>>> >>>>>>> The existing drmm_connector_hdmi_init() helper currently takes >>>>>>> individual capability arguments such as supported_formats and max_bpc. >>>>>>> Adding more HDMI-specific arguments to that function would not scale >>>>>>> well, so move those values into a dedicated capabilities structure and >>>>>>> implement the existing helper as a wrapper around the new caps-based >>>>>>> interface. >>>>>> >>>>>> I think, it was an intention of Maxime: make sure that every driver is >>>>>> forced to provide some values here. With the struct-based init it is >>>>>> easy to overlook or to ommit a value. >>>>> >>>>> Agreed that the struct-based init loses the compile-time guarantee that every >>>>> argument is explicitly provided - that's a real downside. >>>>> >>>>> I'd argue it's recoverable, though: the init helper validates the mandatory >>>>> fields, so a driver that omits a required value gets rejected at init time >>>>> rather than silently misconfigured. The "you must provide sane values" property >>>>> is expected to be preserved, just enforced at runtime instead of by the >>>>> compiler. >>>> >>>> Yeah, I don't think we can win with C here. Rust might, but we're >>>> probably a long way from that. >>>> >>>>> The main motivation for the struct is scalability/maintainability as we add HDMI >>>>> 2.x capabilities: new fields go into the struct rather than growing the helper's >>>>> argument list, so existing callers don't need churny signature updates on every >>>>> extension. >>>>> >>>>> FWIW, in the previous revision we discussed addressing the concern with a >>>>> callback instead. Sadly, I had to discard that approach, as it proved not >>>>> flexible enough, e.g. drm_bridge_connector_init() computes caps dynamically, and >>>>> would have required either stateful callbacks, or storing redundant/temporary >>>>> cap data in driver-private structures just to satisfy the callback. >>>> >>>> I just realized something reviewing your patch: we don't necessarily >>>> need an extra argument or a callback, we can just put these fields into >>>> drm_hdmi_connector_funcs directly, and then validate them in init. >>> >>> If I understand correctly, we should drop the drm_connector_hdmi_caps struct >>> introduced by this patch and move all its fields into drm_hdmi_connector_funcs. >>> >>> In that case, how should we proceed with drmm_connector_hdmi_init()? >> >> Actually, this brings us to the callback issue: we cannot compute caps >> dynamically, as it only works with static data, since funcs is supposed to be >> immutable. > > Does it? The core and helpers must consider it immutable but it doesn't > have to. drm_bridge_connector for example could totally allocate it and > dynamically create it based on the bridge capabilities. If we take the VC4 case, is it fine to drop the const from the static drm_connector_hdmi_funcs to allow dynamically setting up supported_hdmi_ver and max_bpc in vc4_hdmi_connector_init()? static struct drm_connector_hdmi_funcs vc4_hdmi_hdmi_connector_funcs = { .tmds_char_rate_valid = vc4_hdmi_connector_clock_valid, ... } static int vc4_hdmi_connector_init() { ... if (vc4_hdmi->variant->supports_hdr) vc4_hdmi_hdmi_connector_funcs.max_bpc = 12; if (vc4_hdmi->variant->max_pixel_clock >= HDMI_2_0_TMDS_CHAR_RATE_MAX_HZ) vc4_hdmi_hdmi_connector_funcs.supported_hdmi_ver = HDMI_VERSION_2_0; else if (vc4_hdmi->variant->max_pixel_clock >= HDMI_1_3_TMDS_CHAR_RATE_MAX_HZ) vc4_hdmi_hdmi_connector_funcs.supported_hdmi_ver = HDMI_VERSION_1_3; ... } >> Moreover, we would end up with some redundancy, as most of these input fields, >> after validation, would be stored (altered or not) directly in >> drm_connector/drm_connector_hdmi structs. > > I mean, part of the conversion would obviously be to remove the > redundant fields. Ack.