linux-kernel - Re: [PATCH V3 1/3] vfio, platform: add support for ACPI while detecting the reset driver

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Date:	Tue, 29 Mar 2016 06:59:15 -0400
From:	okaya@...eaurora.org
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
	timur@...eaurora.org, cov@...eaurora.org, jcm@...hat.com,
	eric.auger@...aro.org, mark.rutland@....com,
	devicetree@...r.kernel.org,
	Baptiste Reynal <b.reynal@...tualopensystems.com>,
	vikrams@...eaurora.org, marc.zyngier@....com,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	vinod.koul@...el.com, Alex Williamson <alex.williamson@...hat.com>,
	agross@...eaurora.org, Dan Carpenter <dan.carpenter@...cle.com>,
	shankerd@...eaurora.org
Subject: Re: [PATCH V3 1/3] vfio, platform: add support for ACPI while
 detecting the reset driver

On 2016-03-29 05:25, Arnd Bergmann wrote:
> On Monday 28 March 2016 09:35:22 Sinan Kaya wrote:
>> The code is using the compatible DT string to associate a reset driver 
>> with
>> the actual device itself. The compatible string does not exist on ACPI
>> based systems. HID is the unique identifier for a device driver 
>> instead.
>> The change allows a driver to register with DT compatible string or 
>> ACPI
>> HID and then match the object with one of these conditions.
>> 
>> Rules for loading the reset driver are as follow:
>> - ACPI HID needs match for ACPI systems
>> - DT compat needs to match for OF systems
>> 
>> Tested-by: Eric Auger <eric.auger@...aro.org> (device tree only)
>> Tested-by: Shanker Donthineni <shankerd@...eaurora.org> (ACPI only)
>> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
>> 
> 
> 
> This really feels wrong for two reasons:
> 
> * device assignment of non-PCI devices is really special and doesn't
>   seem to make sense on general purpose servers that would be the 
> target
>   for ACPI normally


Why is it special? Acpi is not equal to pci. Platform devices are first 
class devices too. Especially, _cls was introduced for this reason.


> 
> * If there is indeed a requirement for ACPI to handle something like 
> this,
>   it should be part of the ACPI spec, with a well-defined method of 
> handling
>   reset, rather than having to add a device specific hack for each
>   device separately.
> 

I see. Normally, this is done by calling _rst method. AFAIK, Linux 
doesn’t support _rst. I can check its presence and call it if it is 
there.



> 	Arnd