linux-kernel - Re: [PATCH v2] nvmem: rmem: Fix return value of rmem

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Message-ID: <CAOSNQF1_7p61pgGBcb0QWmCLCBfNAk2-gQ4qFybfbbxON3n5pw@mail.gmail.com>
Date: Tue, 27 Feb 2024 14:01:25 +0530
From: Joy Chakraborty <joychakr@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>, Rob Herring <robh@...nel.org>, 
	Nicolas Saenz Julienne <nsaenz@...nel.org>, linux-kernel@...r.kernel.org, manugautam@...gle.com, 
	stable@...r.kernel.org
Subject: Re: [PATCH v2] nvmem: rmem: Fix return value of rmem_read()

On Tue, Feb 27, 2024 at 1:02 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Tue, Feb 27, 2024 at 12:27:09PM +0530, Joy Chakraborty wrote:
> > On Wed, Feb 7, 2024 at 8:33 PM Joy Chakraborty <joychakr@...glecom> wrote:
> > >
> > > On Wed, Feb 7, 2024 at 3:04 PM Greg Kroah-Hartman
> > > <gregkh@...uxfoundation.org> wrote:
> > > >
> > > > On Tue, Feb 06, 2024 at 05:22:15PM +0530, Joy Chakraborty wrote:
> > > > > > > Userspace will see a false error with nvmem cell reads from
> > > > > > > nvmem_cell_attr_read() in current code, which should be fixed on
> > > > > > > returning 0 for success.
> > > > > >
> > > > > > So maybe fix this all up to allow the read to return the actual amount
> > > > > > read?  That feels more "correct" to me.
> > > > > >
> > > > >
> > > > > If I change the behavior of the nvmem_reg_read_t callback to negative
> > > > > for error and number of bytes actually read for success then, other
> > > > > than the core driver I would also have to change all the
> > > > > nvmem-provider drivers.
> > > > > Is it okay to do so ?
> > > >
> > > > Sure, why not?  That seems like the correct fix to me, right?
> > >
> > > Sure, I can do that.
> > >
> > > Is it okay to change the if checks on the return code to "if (rc < 0)"
> > > instead of "if (rc)" as a fix for the immediate issue with how return
> > > value from rmem is handled which can be applied to older kernels.
> > > In a separate patch I can change the definition of nvmem_reg_read_t()
> > > to return ssize_t instead of int and make corresponding changes to
> > > nvmem-provider drivers.
> > >
> > > Does that sound okay ?
> >
> > Hi Greg,
> >
> > Sent a patch https://lore.kernel.org/all/20240219113149.2437990-2-joychakr@google.com/
> > to change the return type for read/write callbacks.
> > Do I mark that with the "Fixes:" tag as well ?
>
> Is it actually fixing a bug?  Or just evolving the api to be more
> correct over time?  I think the latter.

It is more of the latter i.e. evolving the API to be correct but
indirectly it ends up fixing this bug where positive value returned by
this rmem driver is treated as an error in nvmem core.

>
> > It affects a lot of files so might not be able to easily pick to an
> > older kernel when needed.
>
> What is it fixing that older kernels need?

It is fixing the handling of a positive value returned by this rmem
driver which will be treated as an error in older kernels as the nvmem
core expects 0 on success without changing API behavior.

>
> And do not worry about stable kernels while doing development, only
> take that into consideration after your changes are accepted.

Got it, thank you for your input .

>
> thanks,
>
> greg k-h

Thanks
Joy