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

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Date:	Wed, 16 Mar 2016 10:27:24 -0400
From:	Sinan Kaya <okaya@...eaurora.org>
To:	Eric Auger <eric.auger@...aro.org>, kvm@...r.kernel.org,
	timur@...eaurora.org, cov@...eaurora.org, jcm@...hat.com,
	Baptiste Reynal <b.reynal@...tualopensystems.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 Baptiste,

>> 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.

Are you OK with requiring reset driver for AMBA devices too? The PL330 
driver won't work until a reset driver is submitted for it.

>>
>> 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.

I can see this flag useful for testing purposes but it should not be used in 
production.

How about I add a module parameter which is not set by default? When set,
I don't perform the reset requirement check.

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

OK, no rush.

> 
> Best Regards
> 
> Eric
> 


-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project