From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 71BA1C433EF for ; Mon, 28 Feb 2022 08:03:44 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id BCC9110E215; Mon, 28 Feb 2022 08:03:43 +0000 (UTC) Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) by gabe.freedesktop.org (Postfix) with ESMTPS id 567B710E215; Mon, 28 Feb 2022 08:03:42 +0000 (UTC) Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id B7030478; Mon, 28 Feb 2022 09:03:40 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1646035420; bh=5iPsVVkV+UW1rtaXLUQ9WJIZjzFugp1+ZIHB3gAZH/I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=HvbFI+ywFr3p+aX7+bhCGkcaC4q+7rWP3Ry22x1zrX2RIxdur28jLXGwpwZWzaQXN q8DXqhdni/2XLowhQH2Fb2t3sSEQxziLlJAnv0IT638bFhMmj2xBxzlWFiBHcoZV+H A7DGfY9Vu0C2MlmVTW+KdgJuNla6MBD65IVeO0dM= Date: Mon, 28 Feb 2022 10:03:29 +0200 From: Laurent Pinchart To: Rob Clark Message-ID: References: <20220202085429.22261-1-suraj.kandpal@intel.com> <20220202085429.22261-6-suraj.kandpal@intel.com> <87y22ts948.fsf@intel.com> <87v8xxs2hz.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Subject: Re: [Intel-gfx] [PATCH 5/6] drm/rcar_du: changes to rcar-du driver resulting from drm_writeback_connector structure changes X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Carsten Haitzler , Jani Nikula , Intel Graphics Development , Abhinav Kumar , dri-devel , Dmitry Baryshkov Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Hi Rob, On Sat, Feb 26, 2022 at 10:27:59AM -0800, Rob Clark wrote: > On Wed, Feb 2, 2022 at 7:41 AM Jani Nikula wrote: > > On Wed, 02 Feb 2022, Laurent Pinchart wrote: > > > On Wed, Feb 02, 2022 at 03:15:03PM +0200, Jani Nikula wrote: > > >> On Wed, 02 Feb 2022, Laurent Pinchart wrote: > > >> > On Wed, Feb 02, 2022 at 02:24:28PM +0530, Kandpal Suraj wrote: > > >> >> Changing rcar_du driver to accomadate the change of > > >> >> drm_writeback_connector.base and drm_writeback_connector.encoder > > >> >> to a pointer the reason for which is explained in the > > >> >> Patch(drm: add writeback pointers to drm_connector). > > >> >> > > >> >> Signed-off-by: Kandpal Suraj > > >> >> --- > > >> >> drivers/gpu/drm/rcar-du/rcar_du_crtc.h | 2 ++ > > >> >> drivers/gpu/drm/rcar-du/rcar_du_writeback.c | 8 +++++--- > > >> >> 2 files changed, 7 insertions(+), 3 deletions(-) > > >> >> > > >> >> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.h b/drivers/gpu/drm/rcar-du/rcar_du_crtc.h > > >> >> index 66e8839db708..68f387a04502 100644 > > >> >> --- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.h > > >> >> +++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.h > > >> >> @@ -72,6 +72,8 @@ struct rcar_du_crtc { > > >> >> const char *const *sources; > > >> >> unsigned int sources_count; > > >> >> > > >> >> + struct drm_connector connector; > > >> >> + struct drm_encoder encoder; > > >> > > > >> > Those fields are, at best, poorly named. Furthermore, there's no need in > > >> > this driver or in other drivers using drm_writeback_connector to create > > >> > an encoder or connector manually. Let's not polute all drivers because > > >> > i915 doesn't have its abstractions right. > > >> > > >> i915 uses the quite common model for struct inheritance: > > >> > > >> struct intel_connector { > > >> struct drm_connector base; > > >> /* ... */ > > >> } > > >> > > >> Same with at least amd, ast, fsl-dcu, hisilicon, mga200, msm, nouveau, > > >> radeon, tilcdc, and vboxvideo. > > >> > > >> We could argue about the relative merits of that abstraction, but I > > >> think the bottom line is that it's popular and the drivers using it are > > >> not going to be persuaded to move away from it. > > > > > > Nobody said inheritance is bad. > > > > > >> It's no coincidence that the drivers who've implemented writeback so far > > >> (komeda, mali, rcar-du, vc4, and vkms) do not use the abstraction, > > >> because the drm_writeback_connector midlayer does, forcing the issue. > > > > > > Are you sure it's not a coincidence ? :-) > > > > > > The encoder and especially connector created by drm_writeback_connector > > > are there only because KMS requires a drm_encoder and a drm_connector to > > > be exposed to userspace (and I could argue that using a connector for > > > writeback is a hack, but that won't change). The connector is "virtual", > > > I still fail to see why i915 or any other driver would need to wrap it > > > into something else. The whole point of the drm_writeback_connector > > > abstraction is that drivers do not have to manage the writeback > > > drm_connector manually, they shouldn't touch it at all. > > > > The thing is, drm_writeback_connector_init() calling > > drm_connector_init() on the drm_connector embedded in > > drm_writeback_connector leads to that connector being added to the > > drm_device's list of connectors. Ditto for the encoder. > > > > All the driver code that handles drm_connectors would need to take into > > account they might not be embedded in intel_connector. Throughout the > > driver. Ditto for the encoders. > > The assumption that a connector is embedded in intel_connector doesn't > really play that well with how bridge and panel connectors work.. so > in general this seems like a good thing to unwind. > > But as a point of practicality, i915 is a large driver covering a lot > of generations of hw with a lot of users. So I can understand > changing this design isn't something that can happen quickly or > easily. IMO we should allow i915 to create it's own connector for > writeback, and just document clearly that this isn't the approach new > drivers should take. I mean, I understand idealism, but sometimes a > dose of pragmatism is needed. :-) i915 is big, but so is Intel. It's not fair to treat everybody else as a second class citizen and let Intel get away without doing its homework. I want to see this refactoring effort moving forward in i915 (and moving to drm_bridge would then be a good idea too). If writeback support in i915 urgent, then we can discuss *temporary* pragmatic stopgap measures, but not without a real effort to fix the core issue. > > The point is, you can't initialize a connector or an encoder for a > > drm_device in isolation of the rest of the driver, even if it were > > supposed to be hidden away. -- Regards, Laurent Pinchart