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 X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C9926C4338F for ; Tue, 10 Aug 2021 10:33:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AA45460EB7 for ; Tue, 10 Aug 2021 10:33:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239045AbhHJKdf convert rfc822-to-8bit (ORCPT ); Tue, 10 Aug 2021 06:33:35 -0400 Received: from aposti.net ([89.234.176.197]:47300 "EHLO aposti.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238459AbhHJKdf (ORCPT ); Tue, 10 Aug 2021 06:33:35 -0400 Date: Tue, 10 Aug 2021 12:33:04 +0200 From: Paul Cercueil Subject: Re: [PATCH 2/2] gpu/drm: ingenic: Add workaround for disabled drivers To: Daniel Vetter Cc: Greg Kroah-Hartman , Rob Herring , "Rafael J . Wysocki" , David Airlie , Sam Ravnborg , list@opendingux.net, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, dri-devel@lists.freedesktop.org Message-Id: <4BDMXQ.S6A97ME8XJUV@crapouillou.net> In-Reply-To: References: <20210805192110.90302-1-paul@crapouillou.net> <20210805192110.90302-3-paul@crapouillou.net> <3HUDXQ.7RBGD4FUHR2F@crapouillou.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Hi Daniel, Le mar., août 10 2021 at 11:35:43 +0200, Daniel Vetter a écrit : > On Fri, Aug 06, 2021 at 01:01:33PM +0200, Paul Cercueil wrote: >> Hi Greg, >> >> Le ven., août 6 2021 at 12:17:55 +0200, Greg Kroah-Hartman >> a écrit : >> > On Thu, Aug 05, 2021 at 10:05:27PM +0200, Paul Cercueil wrote: >> > > Hi Greg, >> > > >> > > Le jeu., août 5 2021 at 21:35:34 +0200, Greg Kroah-Hartman >> > > a écrit : >> > > > On Thu, Aug 05, 2021 at 09:21:09PM +0200, Paul Cercueil >> wrote: >> > > > > When the drivers of remote devices (e.g. HDMI chip) are >> > > disabled in >> > > > > the >> > > > > config, we want the ingenic-drm driver to be able to probe >> > > > > nonetheless >> > > > > with the other devices (e.g. internal LCD panel) that are >> > > enabled. >> > > > > >> > > > > Signed-off-by: Paul Cercueil >> > > > > --- >> > > > > drivers/gpu/drm/ingenic/ingenic-drm-drv.c | 12 >> ++++++++++++ >> > > > > 1 file changed, 12 insertions(+) >> > > > > >> > > > > diff --git a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c >> > > > > b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c >> > > > > index d261f7a03b18..5e1fdbb0ba6b 100644 >> > > > > --- a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c >> > > > > +++ b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c >> > > > > @@ -1058,6 +1058,18 @@ static int ingenic_drm_bind(struct >> > > device >> > > > > *dev, bool has_components) >> > > > > for (i = 0; ; i++) { >> > > > > ret = drm_of_find_panel_or_bridge(dev->of_node, 0, i, >> > > &panel, >> > > > > &bridge); >> > > > > if (ret) { >> > > > > + /* >> > > > > + * Workaround for the case where the drivers for the >> > > > > + * remote devices are not enabled. When that happens, >> > > > > + * drm_of_find_panel_or_bridge() returns -EPROBE_DEFER >> > > > > + * endlessly, which prevents the ingenic-drm driver >> from >> > > > > + * working at all. >> > > > > + */ >> > > > > + if (ret == -EPROBE_DEFER) { >> > > > > + ret = driver_deferred_probe_check_state(dev); >> > > > > + if (ret == -ENODEV || ret == -ETIMEDOUT) >> > > > > + continue; >> > > > > + } >> > > > >> > > > So you are mucking around with devices on other busses >> within this >> > > > driver? What could go wrong? :( >> > > >> > > I'm doing the same thing as everybody else. This is the DRM >> driver, >> > > and >> > > there is a driver for the external HDMI chip which gives us a >> DRM >> > > bridge >> > > that we can obtain from the device tree. >> > >> > But then why do you need to call this function that is there for >> a bus, >> > not for a driver. >> >> The documentation disagrees with you :) >> >> And, if that has any weight, this solution was proposed by Rob. >> >> > > > Please use the existing driver core functionality for this >> type of >> > > > thing, it is not unique, no need for this function to be >> called. >> > > >> > > I'm not sure you understand what I'm doing here. This driver >> calls >> > > drm_of_find_panel_or_bridge(), without guarantee that the >> driver >> > > for the >> > > remote device (connected via DT graph) has been enabled in the >> > > kernel >> > > config. In that case it will always return -EPROBE_DEFER and >> the >> > > ingenic-drm >> > > driver will never probe. >> > > >> > > This patch makes sure that the driver can probe if the HDMI >> driver >> > > has been >> > > disabled in the kernel config, nothing more. >> > >> > That should not be an issue as you do not care if the config is >> enabled, >> > you just want to do something in the future if the driver shows >> up, >> > right? >> >> Well, the DRM subsystem doesn't really seem to handle hotplug of >> hardware. >> Right now all the drivers for the connected hardware need to probe >> before >> the main DRM driver. So I need to know that a remote device >> (connected via >> DT graph) will never probe. >> >> Give me a of_graph_remote_device_driver_will_never_probe() and I'll >> use >> that. >> >> > Much like the device link code, have you looked at that? >> >> I don't see how that would help in any way. The device link code >> would allow >> me to set a dependency between the remote hardware (HDMI chip, >> provider) and >> the LCD controller (consumer), but I already have that dependency >> though the >> DT graph. What I need is a way for the consumer to continue probing >> if the >> provider is not going to probe. > > Is this actually a legit use-case? > > Like you have hw with a bunch of sub-devices linked, and you decided > to > disable some of them, which makes the driver not load. Yes. I'm facing that issue with a board that has a LCD panel and a HDMI controller (IT66121). I have a "flasher" program for all the Ingenic boards, that's basically just a Linux kernel + initramfs booted over USB (device). I can't realistically enable every single driver for all the hardware that's on these boards while still having a tiny footprint. And I shouldn't have to care about it either. > Why should we care? Is that hdmi driver really that big that we have > to > support this use-case? DRM maintainers work with what embedded devs would call "infinite resources". It annoys me that CONFIG_DRM pulls the I2C code even though I may just have a LCD panel, and it annoys me that I have to enable support for hardware that I'm not even planning to use, just so that the DRM driver works for the hardware I do want to use. > I know it's possible to do this, that doesn't mean it's a good idea. > There's inifinitely more randconfigs that don't boot on my machine > here > for various reasons than the ones that do boot. We don't have "fixes" > for > all of these to make things still work, despite user misconfiguring > their > kernel. I understand, you can't really expect random configs to work every time. But it should still be possible to disable drivers for *optional* hardware in the config and end up with a working system. Cheers, -Paul