linux-kernel - Re: [Qemu-devel] SCSI bus failures with qemu-arm in kernel 3.8+

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Date:	Thu, 15 Aug 2013 19:05:22 +0100
From:	Peter Maydell <peter.maydell@...aro.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	QEMU Developers <qemu-devel@...gnu.org>,
	Arnd Bergmann <arnd.bergmann@...aro.org>
Subject: Re: [Qemu-devel] SCSI bus failures with qemu-arm in kernel 3.8+

On 15 August 2013 18:54, Guenter Roeck <linux@...ck-us.net> wrote:
> On Thu, Aug 15, 2013 at 05:45:42PM +0100, Peter Maydell wrote:
>> On 13 August 2013 04:40, Guenter Roeck <linux@...ck-us.net> wrote:
>> > Patch tested and working with qemu 1.5.2, using the configuration file
>> > from the yocto project. Patch applied on top of kernel version 3.11-rc5.
>>
>> OK, I tested this on PB926+PCI backplane hardware, and it is
>> definitely better than current mainline, in that the test USB
>> card that I have no longer causes the kernel to generate this sort of
>> backtrace:
>>
> Do you mean my patch fixes the traceback below as a side effect ?
> Would be great ... it would be one more reason to get it applied.

Yes, exactly -- the kernel currently has the wrong irq mapping,
which causes the traceback (ie h/w asserts irq 93 but the kernel
is listening on something else). That the patch fixes this confirms
that it is the behaviour of hardware as well as of QEMU.

>> However it still doesn't seem to reliably detect the USB harddisk
>> plugged into the card, so I think there may be further issues, possibly
>> some subset of those Arnd identified and fixed with this patch:
>> http://permalink.gmane.org/gmane.linux.ports.arm.kernel/93397
>>
> Does it get better if you apply Arnd's patch ?

Arnd's patch is ancient and won't apply as is (due to intervening
changes and also because some of the things it fixes were fixed
in later patches); I'm currently trying to extract the relevant parts.

If you want you can confirm that I/O port PCI access is broken on
QEMU too -- disable CONFIG_SCSI_SYM53C8XX_MMIO so
the driver uses PCI IO rather than MMIO and you'll see QEMU's
SCSI device doesn't work any more.

>> so I'd like to continue testing.
>>
>> The other thing this patch should (IMHO) have is the
>> line in pci_versatile_setup() which tells QEMU that the
>> kernel really does expect hardware-like behaviour:

>> (Without this line QEMU will guess whether the kernel is broken
>> or not and will get it right most but not necessarily all of the time.)
>>
> Might make sense, but I think it should be a separate patch.

It needs to go in the same patch, because a kernel with the fixed
irq remapping must also tell QEMU it is fixed; if you split the
two then at the point between the two patches the kernel is
broken for bisection purposes.

> If I understand correctly, my patch fixes the SCSI problem.
> Is that correct ? If so, can we get it applied to mainline ?

I'd rather get to a point where I have the hardware definitely
completely working first. There's no real hurry, this has been
broken for months and months.

-- PMM
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