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Subject: Re: [RFC PATCH 00/35] Move all PCIBIOS* definitions into arch/x86
From:   Benjamin Herrenschmidt <benh@kernel.crashing.org>
To:     Bjorn Helgaas <helgaas@kernel.org>, Arnd Bergmann <arnd@arndb.de>
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Date:   Wed, 15 Jul 2020 12:19:46 +1000
In-Reply-To: <20200714234625.GA428442@bjorn-Precision-5520>
References: <20200714234625.GA428442@bjorn-Precision-5520>
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On Tue, 2020-07-14 at 18:46 -0500, Bjorn Helgaas wrote:
> Yes.  I have no problem with that.  There are a few cases where it's
> important to check for errors, e.g., we read a status register and do
> something based on a bit being set.  A failure will return all bits
> set, and we may do the wrong thing.  But most of the errors we care
> about will be on MMIO reads, not config reads, so we can probably
> ignore most config read errors.

And in both cases, we don't have the plumbing to provide accurate
and reliable error returns for all platforms anyways (esp. not for
MMIO).

I think it makes sense to stick to the good old "if all 1's, then go
out of line" including for config space.

 ../..

> Yep, except for things like device removal or other PCI errors.

A whole bunch of these are reported asynchronously, esp for writes (and
yes, including config writes, they are supposed to be non-posted but
more often than not, the path  from the CPU to the PCI bridge remains
posted for writes including config ones).

> So maybe a good place to start is by removing some of the useless
> error checking for pci_read_config_*() and pci_write_config_*().
> That's a decent-sized but not impractical project that could be done
> per subsystem or something:
> 
>   git grep -E "(if|return|=).*\<pci_(read|write)_config" drivers
> 
> finds about 400 matches.
> 
> Some of those callers probably really *do* want to check for errors,
> and I guess we'd have to identify them and do them separately as you
> mentioned.

I'd be curious about these considering how unreliable our error return
is accross the board.

Cheers,
Ben.