linux-kernel - Re: [PATCH v2] bus: mvebu-mbus: Avoid setting an undefined window size

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Message-ID: <20140409075624.GA17071@1wt.eu>
Date:	Wed, 9 Apr 2014 09:56:24 +0200
From:	Willy Tarreau <w@....eu>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Neil Greatorex <neil@...boyfat.co.uk>,
	linux-arm-kernel@...ts.infradead.org,
	Matthew Minter <matthew_minter@...atex.com>,
	linux-kernel@...r.kernel.org, Jason Cooper <jason@...edaemon.net>
Subject: Re: [PATCH v2] bus: mvebu-mbus: Avoid setting an undefined window size

On Wed, Apr 09, 2014 at 09:53:50AM +0200, Thomas Petazzoni wrote:
> Dear Willy Tarreau,
> 
> On Wed, 9 Apr 2014 09:47:52 +0200, Willy Tarreau wrote:
> 
> > > Yes, the panic is expected: Jason's patch is not *fixing* anything,
> > > it's just telling you *why* it's going to panic.
> > 
> > I just thought that the EINVAL would prevent one from registering
> > the device, which would be more useful (if at all possible).
> 
> Unfortunately, I don't think that's possible: the function that sets up
> the MBus window is called by the emulated bridge code, i.e when the
> Linux PCI core thinks it is doing a write to a bridge register. And I
> don't think there is a way of "refusing" the write to let the Linux
> PCI core know that it was not possible to set up the bridge BAR as it
> was requested.
> 
> Maybe this is something that Jason can confirm/infirm. I remember
> having a quick look at the core Linux PCI core to see if it was
> somehow checking whether the bridge BAR has been properly configured,
> but I think I concluded it was not the case, and it was just assuming
> that write the memory base/limit in the bridge registers was
> sufficient. 

OK thanks for the detailed explanation!

Willy

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