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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E76E7C433EF for ; Fri, 28 Jan 2022 10:34:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233576AbiA1Kec (ORCPT ); Fri, 28 Jan 2022 05:34:32 -0500 Received: from perceval.ideasonboard.com ([213.167.242.64]:38006 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232120AbiA1Ke2 (ORCPT ); Fri, 28 Jan 2022 05:34:28 -0500 Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 6A6D3B9C; Fri, 28 Jan 2022 11:34:26 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1643366066; bh=SjngVim/bAf9eBc4Da9VVdDH4QW1J82EoUqAY4mOegc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=iIqVB+7jiNvEi7UPEfL67GXviPPO5/o3PB4DBuzEpg9fSbb0AATxZL2mqIDQQcANj v8v6AmI/srfB2KUotIg5IvS35m/GHPvurjFIJ/DRqeC88pmKvnGJq1JNfpGDtYVANf zvAnZ2+TEMafOBeJESYCAfNJMA7aGxI2yv4UD+ac= Date: Fri, 28 Jan 2022 12:34:05 +0200 From: Laurent Pinchart To: Thomas Zimmermann Cc: Kieran Bingham , Javier Martinez Canillas , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 31/37] drm: rcar-du: Add support for the nomodeset kernel parameter Message-ID: References: <20211217003752.3946210-1-javierm@redhat.com> <20211217003752.3946210-32-javierm@redhat.com> <164336121612.533872.1685181669511488706@Monstersaurus> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Thomas, On Fri, Jan 28, 2022 at 10:33:21AM +0100, Thomas Zimmermann wrote: > Am 28.01.22 um 10:13 schrieb Kieran Bingham: > > Quoting Javier Martinez Canillas (2021-12-17 00:37:46) > >> According to disable Documentation/admin-guide/kernel-parameters.txt, this > >> parameter can be used to disable kernel modesetting. > >> > >> DRM drivers will not perform display-mode changes or accelerated rendering > >> and only the system framebuffer will be available if it was set-up. > > > > What is the 'system framebuffer' in this instance? Reading > > https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt > > it sounds like that means anything already set up by the bootloader. > > Exactly this. > > >> But only a few DRM drivers currently check for nomodeset, make this driver > >> to also support the command line parameter. > >> > >> Signed-off-by: Javier Martinez Canillas > >> --- > >> > >> (no changes since v1) > >> > >> drivers/gpu/drm/rcar-du/rcar_du_drv.c | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c > >> index 5a8131ef81d5..982e450233ed 100644 > >> --- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c > >> +++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c > >> @@ -701,6 +701,9 @@ static struct platform_driver rcar_du_platform_driver = { > >> > >> static int __init rcar_du_init(void) > >> { > >> + if (drm_firmware_drivers_only()) > >> + return -ENODEV; > >> + > > > > This will completely disable all control of the display device when > > nomodeset is enabled. > > > > Is there any requirement for us to support outputting to the display if > > it was previously set up? presumably without setting or changing any > > modes, but simply allowing the existing frame to be updated? > > There's no requirement for your driver. We just want a parameter where > we can conveniently disable most of DRM's drivers and reduce it to a > minimum. Helps distributions to provide a simple fallback mode. Most > PCI-based drivers already support that. Now we're added it to the other > drivers as well. > > > > > I think the implication is that 'firmware drivers' would mean a display > > could be updated through some firmware interface, which we won't have > > ... so it seems reasonable to accept that this whole driver can be > > disabled in that instance. > > It cannot be 'mode-setted'. We get a pre-configured framebuffer from the > firmware or bootloader. Whatever we draw there shows up on the screen. I doubt that's going to work as you expect, clocks and regulators will get disabled at boot if not used by any driver. > > Reading your mail that brought this thread up in my inbox, I think > > you've already hit merge on this, so don't worry about adding a tag in > > that instance, but I think this is ok. > > > > Reviewed-by: Kieran Bingham > > > >> rcar_du_of_init(rcar_du_of_table); > >> > >> return platform_driver_register(&rcar_du_platform_driver); -- Regards, Laurent Pinchart