linux-kernel - Re: [PATCH V6 5/8] vfio: platform: call

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Message-ID: <575E2B50.3040000@codeaurora.org>
Date:	Sun, 12 Jun 2016 23:41:04 -0400
From:	Sinan Kaya <okaya@...eaurora.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	kvm@...r.kernel.org, Timur Tabi <timur@...eaurora.org>,
	Christopher Covington <cov@...eaurora.org>,
	Jon Masters <jcm@...hat.com>, eric.auger@...aro.org,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Andy Gross <agross@...eaurora.org>,
	linux-arm-msm@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Baptiste Reynal <b.reynal@...tualopensystems.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V6 5/8] vfio: platform: call _RST method when using ACPI

On 6/8/2016 6:31 PM, Rafael J. Wysocki wrote:
> On Sun, May 29, 2016 at 12:01 AM, Sinan Kaya <okaya@...eaurora.org> wrote:
>> The device tree code checks for the presence of a reset driver and calls
>> the of_reset function pointer by looking up the reset driver as a module.
>>
>> ACPI defines _RST method to perform device level reset. After the _RST
>> method is executed, the OS can resume using the device. _RST method is
>> expected to stop DMA transfers and IRQs.
>>
>> This patch checks the presence of _RST method and calls the _RST
>> method when reset is requested.
> 

A little bit of misinformation here. The current code is checking the presence
during probe time. If the presence of _RST method is required then probe is
aborted. Otherwise, probe will complete execution.

When reset call is to be executed, presence of _RST method is no longer checked.
Instead, the method is directly called. 

I was talking about the contribution of this patch as both here. I'll clarify
the commit message. 

> You could check if _RST is present at probe time and store the ACPI
> handle of it instead of the HID pointer.
> 
> This way you wouldn't need to repeat that check every time reset is used.
> 

Based on the requirement that the code can be executed without the presence
of _RST method for development purposes, I'm hesitant to use the handle of the
reset method as a gating factor.

-- 
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