[PATCH] gpu: host1x: Do not output error message for deferred probe

[Thierry Reding]

On Wed, Jun 05, 2019 at 03:40:28PM +0300, Dmitry Osipenko wrote:
> 05.06.2019 15:32, Thierry Reding пишет:
> > On Wed, Jun 05, 2019 at 02:25:43PM +0300, Dmitry Osipenko wrote:
> >> 05.06.2019 11:28, Thierry Reding пишет:
> >>> On Tue, Jun 04, 2019 at 07:07:42PM +0300, Dmitry Osipenko wrote:
> >>>> 04.06.2019 18:31, Thierry Reding пишет:
> >>>>> From: Thierry Reding <treding at nvidia.com>
> >>>>>
> >>>>> When deferring probe, avoid logging a confusing error message. While at
> >>>>> it, make the error message more informational.
> >>>>>
> >>>>> Signed-off-by: Thierry Reding <treding at nvidia.com>
> >>>>> ---
> >>>>>  drivers/gpu/host1x/dev.c | 5 ++++-
> >>>>>  1 file changed, 4 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/drivers/gpu/host1x/dev.c b/drivers/gpu/host1x/dev.c
> >>>>> index c55e2d634887..5a3f797240d4 100644
> >>>>> --- a/drivers/gpu/host1x/dev.c
> >>>>> +++ b/drivers/gpu/host1x/dev.c
> >>>>> @@ -247,8 +247,11 @@ static int host1x_probe(struct platform_device *pdev)
> >>>>>  
> >>>>>  	host->clk = devm_clk_get(&pdev->dev, NULL);
> >>>>>  	if (IS_ERR(host->clk)) {
> >>>>> -		dev_err(&pdev->dev, "failed to get clock\n");
> >>>>>  		err = PTR_ERR(host->clk);
> >>>>> +
> >>>>> +		if (err != -EPROBE_DEFER)
> >>>>> +			dev_err(&pdev->dev, "failed to get clock: %d\n", err);
> >>>>> +
> >>>>>  		return err;
> >>>>>  	}
> >>>>
> >>>> The clock driver should be available at the time of host1x's probing on
> >>>> all Tegra's because it is one of essential core drivers that become
> >>>> available early during boot.
> >>>
> >>> That's the currently baked-in assumption. However, there can be any
> >>> number of reasons for why the clocks may not show up as early as
> >>> expected, as evidenced in the case of Tegra186.
> >>>
> >>>> I guess you're making this change for T186, is it because the BPMP
> >>>> driver's probe getting deferred? If yes, won't it be possible to fix the
> >>>> defer of the clock driver instead of making such changes in the affected
> >>>> drivers?
> >>>
> >>> The reason why this is now happening on Tegra186 is because the BPMP is
> >>> bound to an IOMMU to avoid getting faults from the new no-bypass policy
> >>> that the ARM SMMU driver is implementing as of v5.2-rc1.
> >>>
> >>> As a result of binding to an IOMMU, the first probe of the BPMP driver
> >>> will get deferred, so any driver trying to request a clock after that
> >>> and before BPMP gets probed successfully the next time, any clk_get()
> >>> calls will fail with -EPROBE_DEFER.
> >>>
> >>> This is a bit unfortunate, but like I said, these kinds of things can
> >>> happen, and probe deferral was designed specifically to deal with that
> >>> kind of situation so that we wouldn't have to rely on all of these
> >>> built-in assumptions that occasionally break.
> >>>
> >>> The driver also already handles deferred probe properly. The only thing
> >>> that this patch really changes is to no longer consider -EPROBE_DEFER an
> >>> error. It's in fact a pretty common situation in many drivers and should
> >>> not warrant a kernel log message.
> >>
> >> You're trying to mask symptoms instead of curing the decease and it looks
> >> like the decease could be cured.
> > 
> > There's nothing here to cure. -EPROBE_DEFER was designed specifically to
> > avoid having to play these kinds of games with initcall levels.
> > 
> > What this patch tries to do is just to avoid printing an error message
> > for something that is not an error. -EPROBE_DEFER is totally expected to
> > happen, it's normal, it's not something that we should bother users with
> > because things end up sorting themselves out in the end.
> > 
> >> Won't something like this work for you?
> > 
> > I'm sure we could find a number of ways to fix this. But there's no need
> > to fix this because it's not broken. What is broken is that we output an
> > error message when this happens and make an elephant out of a fly.
> 
> Sure, this is absolutely not critical and deferred probe is doing its job.
> But don't you agree that it's better to fix the root of the annoyance once
> and for all?

From my point of view deferred probe is the once and for all fix. Back
before we had deferred probe, doing these kinds of initcall reordering
tricks was fairly common and while such a change may fix one setup, it
often ended up breaking others.

Sorry, this is a lesson that we already learned a couple of years ago,
no need to rehash it.

Thierry
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: not available
URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20190605/d3ac01d9/attachment.sig>