linux-kernel - Re: [PATCH v2 0/3] Devres optimization with bound devices

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Message-ID: <872604E6-9C11-4338-95F3-2ECF20AE3309@nvidia.com>
Date: Wed, 30 Apr 2025 12:56:49 +0000
From: Joel Fernandes <joelagnelf@...dia.com>
To: Alexandre Courbot <acourbot@...dia.com>
CC: Danilo Krummrich <dakr@...nel.org>, "gregkh@...uxfoundation.org"
	<gregkh@...uxfoundation.org>, "rafael@...nel.org" <rafael@...nel.org>,
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Subject: Re: [PATCH v2 0/3] Devres optimization with bound devices



> On Apr 29, 2025, at 10:46 PM, Alexandre Courbot <acourbot@...dia.com> wrote:
> 
> On Mon Apr 28, 2025 at 11:00 PM JST, Danilo Krummrich wrote:
>> This patch series implements a direct accessor for the data stored within
>> a Devres container for cases where we can prove that we own a reference
>> to a Device<Bound> (i.e. a bound device) of the same device that was used
>> to create the corresponding Devres container.
>> 
>> Usually, when accessing the data stored within a Devres container, it is
>> not clear whether the data has been revoked already due to the device
>> being unbound and, hence, we have to try whether the access is possible
>> and subsequently keep holding the RCU read lock for the duration of the
>> access.
>> 
>> However, when we can prove that we hold a reference to Device<Bound>
>> matching the device the Devres container has been created with, we can
>> guarantee that the device is not unbound for the duration of the
>> lifetime of the Device<Bound> reference and, hence, it is not possible
>> for the data within the Devres container to be revoked.
>> 
>> Therefore, in this case, we can bypass the atomic check and the RCU read
>> lock, which is a great optimization and simplification for drivers.
> 
> Thanks, this removes one of my pain points with the way revocable
> resources were accessed and will allow to write drivers in a much more
> natural way.
> 
> FWIW, the series
> 
> Reviewed-by: Alexandre Courbot <acourbot@...dia.com>

Nice, I like it. Quite a readability improvement too
on the caller side!

Reviewed-by: Joel Fernandes <joelagnelf@...dia.com>

Thanks.