linux-kernel - Re: [PATCH v1] usb: dwc3: core: Add shutdown callback for dwc3

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Message-ID: <d2348b758fa57acf53885b67f066e0a1@codeaurora.org>
Date:   Tue, 30 Mar 2021 15:25:58 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Sandeep Maheswaram <sanm@...eaurora.org>,
        Felipe Balbi <balbi@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, Manu Gautam <mgautam@...eaurora.org>
Subject: Re: [PATCH v1] usb: dwc3: core: Add shutdown callback for dwc3

On 2021-03-30 14:37, Greg Kroah-Hartman wrote:
> On Tue, Mar 30, 2021 at 02:12:04PM +0530, Sandeep Maheswaram wrote:
>> 
>> On 3/26/2021 7:07 PM, Greg Kroah-Hartman wrote:
>> > On Wed, Mar 24, 2021 at 12:57:32AM +0530, Sandeep Maheswaram wrote:
>> > > This patch adds a shutdown callback to USB DWC core driver to ensure that
>> > > it is properly shutdown in reboot/shutdown path. This is required
>> > > where SMMU address translation is enabled like on SC7180
>> > > SoC and few others. If the hardware is still accessing memory after
>> > > SMMU translation is disabled as part of SMMU shutdown callback in
>> > > system reboot or shutdown path, then IOVAs(I/O virtual address)
>> > > which it was using will go on the bus as the physical addresses which
>> > > might result in unknown crashes (NoC/interconnect errors).
>> > >
>> > > Previously this was added in dwc3 qcom glue driver.
>> > > https://patchwork.kernel.org/project/linux-arm-msm/list/?series=382449
>> > > But observed kernel panic as glue driver shutdown getting called after
>> > > iommu shutdown. As we are adding iommu nodes in dwc core node
>> > > in device tree adding shutdown callback in core driver seems correct.
>> > So shouldn't you also remove this from the qcom glue driver at the same
>> > time?  Please submit both as a patch series.
>> >
>> > thanks,
>> >
>> > greg k-h
>> 
>> Hi Greg,
>> 
>> The qcom glue driver patch is not merged yet. I have just mentioned 
>> for it for reference.
> 
> You know that we can not add callbacks for no in-kernel user, so what
> good is this patch for now?
> 

What in-kernel user? Since when does shutdown callback need an in-kernel
user? When you reboot or shutdown a system, it gets called. The reason
why the shutdown callback is needed is provided in the commit text.

Confused,
Sai Prakash Ranjan

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