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 98274C4320A for ; Tue, 10 Aug 2021 11:58:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 72D6660EDF for ; Tue, 10 Aug 2021 11:58:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238345AbhHJL65 convert rfc822-to-8bit (ORCPT ); Tue, 10 Aug 2021 07:58:57 -0400 Received: from aposti.net ([89.234.176.197]:48670 "EHLO aposti.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233167AbhHJL65 (ORCPT ); Tue, 10 Aug 2021 07:58:57 -0400 Date: Tue, 10 Aug 2021 13:58:24 +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: In-Reply-To: References: <20210805192110.90302-1-paul@crapouillou.net> <20210805192110.90302-3-paul@crapouillou.net> <3HUDXQ.7RBGD4FUHR2F@crapouillou.net> <4BDMXQ.S6A97ME8XJUV@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 12:59:53 +0200, Daniel Vetter a écrit : > On Tue, Aug 10, 2021 at 12:33:04PM +0200, Paul Cercueil wrote: >> 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. > > I think this is were things go wrong. > > Either you have a generic image, where all the needed drivers are > included > as modules. > > Or you have a bespoke image, where you just built-in what you actually > needed. Yes, and that's what I want - a kernel with just the minimal number of built-in drivers that I need (so, not the HDMI chip). > Asking for both is a bit much ... > >> > 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. > > No. > > What I'm rejecting is when people add Kconfig knobs for a single > function, > while we have everything else as fairly monolithic dependencies in > drm. > That makes no sense. > > The only requirement for tiny drm that I have is that whomever > proposes > it: > > - does an overall survey and shows that we do actually get rid of the > big > pieces, and not just of the pieces which are easy to make optional > > - has a solid answer to the maintainance cost this will incur. This > one is > very important, because for historical reasons we have a bunch of > optional things like backlight, and the trend is to make them less > optional because a) those are all rather invalid configs anyway b) > no on > has time to review the constant flux of busy-work bugfixes when > something inevitably breaks again > > Thus far all I got from people who want to make drm tiny is some > wishlist > items and stand-alone patches that don't make sense stand-alone. Until > that's fixed and someone invests serious amounts of time here drm > will be > a big behemoth. And that's because we're very much not operating in > an "infinite resource" world, the most constraint supply we have is > contributor, reviewer and maintainer bandwidth. > > Which yes means occasionally things will continue to suck because no > one > cared enough about it yet. Alright, I can totally understand that. >> > 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. > > The thing is, right now that stuff just isn't optional. Except if you > patch your dt, which I think is the other approach that's been > discussed > here. It's not been discussed yet - I think we talked about it a few weeks ago on IRC. DT is supposed to represent the hardware though, and not a specific configuration, which would be policy; so this isn't really the best solution either. Cheers, -Paul