linux-kernel - Re: [Xen-devel] [PATCH 2/2] xen-pciback: Allow enabling/disabling expansion ROM

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Message-ID: <20181203144738.GQ781@mail-itl>
Date:   Mon, 3 Dec 2018 15:47:38 +0100
From:   Marek Marczykowski <marmarek@...isiblethingslab.com>
To:     Jan Beulich <JBeulich@...e.com>
Cc:     Dwayne Litzenberger <dlitz@...tz.net>,
        Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH 2/2] xen-pciback: Allow enabling/disabling
 expansion ROM

On Mon, Dec 03, 2018 at 04:01:07AM -0700, Jan Beulich wrote:
> >>> On 02.12.18 at 18:47, <marmarek@...isiblethingslab.com> wrote:
> > From: Dwayne Litzenberger <dlitz@...tz.net>
> > 
> > Newer AMD GPUs store their initialization routines as bytecode on the
> > ROM.  This fixes the following initialization error inside the VM when
> > doing PCI passthrough:
> > 
> >     radeon 0000:00:05.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0xffff
> >     radeon 0000:00:05.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0xffff
> >     [drm:radeon_get_bios [radeon]] *ERROR* Unable to locate a BIOS ROM
> >     radeon 0000:00:05.0: Fatal error during GPU init
> 
> Isn't it that qemu is supposed to surface the ROM image to guests,
> making it unnecessary to allow guests control over the physical
> enable bit? 

Unless that qemu is in stubdomain, where it use pciback to access
everything about the device...

> Also why would allowing to alter the bit depend on
> whether the address portion of the value is non-zero?

That's a good question. According to commit message I think it should be
a ROM presence check instead. If needed at this point at all - is this
function even called if there is no ROM?

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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