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

[Thierry Reding]

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.

Thierry
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