linux-kernel - Re: [PATCH V2 2/3] vfio, platform: make reset driver a requirement

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Date:	Wed, 16 Mar 2016 05:36:29 +0100
From:	Eric Auger <eric.auger@...aro.org>
To:	Sinan Kaya <okaya@...eaurora.org>, kvm@...r.kernel.org,
	timur@...eaurora.org, cov@...eaurora.org, jcm@...hat.com
Cc:	shankerd@...eaurora.org, vikrams@...eaurora.org,
	marc.zyngier@....com, mark.rutland@....com,
	devicetree@...r.kernel.org, vinod.koul@...el.com,
	agross@...eaurora.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Baptiste Reynal <b.reynal@...tualopensystems.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 2/3] vfio, platform: make reset driver a requirement

Hi Sinan,
On 03/13/2016 06:25 PM, Sinan Kaya wrote:
> On 3/11/2016 11:54 AM, Sinan Kaya wrote:
>> The code was allowing platform devices to be used without a supporting VFIO
>> reset driver. The hardware can be left in some inconsistent state after a
>> guest machine abort.
>>
>> The reset driver will put the hardware back to safe state and disable
>> interrupts before returning the control back to the host machine.
>>
>> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
>> ---
>>  drivers/vfio/platform/vfio_platform_common.c | 16 +++++++++-------
>>  1 file changed, 9 insertions(+), 7 deletions(-)
>>
> I was looking at the code. It looks like this is going to break VFIO AMBA. The
> common implementation is shared with AMBA and platform devices.
> 
> I couldn't see a reset function for AMBA devices.
> 
> Is there anyway to write reset function for it? I have no experience with 
> AMBA devices.
To my knowledge only the PL330 DMA controller (drivers/dma/pl330.c) was
passthrough'ed at some point, rather for development purpose than
production purpose. This was done by Virtual Open Systems (ask Baptiste
for more details). But I don't think this is really used.
> 
> Would you include a reset needed flag and just not require it for AMBA? 
> (I honestly don't like this idea)
> 
I think the requirement also makes sense for AMBA.

Maybe an option would be to add a module parameter that would allow to
use the vfio platform/amba driver without reset module (with explicit
opt-in from the user). Maybe this can be done later on.

FYI I will not have access to my mailbox until the end of the week.

Best Regards

Eric