linux-kernel - Re: [PATCH] staging: media: atomisp: Use kmap_local_page() in hmm

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Date:   Fri, 29 Apr 2022 15:46:47 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tsuchiya Yuto <kitakar@...il.com>
Cc:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Martiros Shakhzadyan <vrzh@...h.net>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>,
        outreachy@...ts.linux.dev
Subject: Re: [PATCH] staging: media: atomisp: Use kmap_local_page() in hmm_store()

On lunedì 25 aprile 2022 20:29:03 CEST Fabio M. De Francesco wrote:
> On giovedì 14 aprile 2022 00:55:31 CEST Fabio M. De Francesco wrote:
> > The use of kmap() is being deprecated in favor of kmap_local_page()
> > where it is feasible. The same is true for kmap_atomic().
> > 
> > In file pci/hmm/hmm.c, function hmm_store() test if we are in atomic
> > context and, if so, it calls kmap_atomic(), if not, it calls kmap().
> > 
> > First of all, in_atomic() shouldn't be used in drivers. This macro
> > cannot always detect atomic context; in particular, it cannot know
> > about held spinlocks in non-preemptible kernels.
> > 
> > Notwithstanding what it is said above, this code doesn't need to care
> > whether or not it is executing in atomic context. It can simply use
> > kmap_local_page() / kunmap_local() that can instead do the mapping /
> > unmapping regardless of the context.
> > 
> > With kmap_local_page(), the mapping is per thread, CPU local and not
> > globally visible. Therefore, hmm_store()() is a function where the use
> > of kmap_local_page() in place of both kmap() and kmap_atomic() is
> > correctly suited.
> > 
> > Convert the calls of kmap() / kunmap() and kmap_atomic() /
> > kunmap_atomic() to kmap_local_page() / kunmap_local() and drop the
> > unnecessary tests which test if the code is in atomic context.
> > 
> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> > ---
> >  drivers/staging/media/atomisp/pci/hmm/hmm.c | 14 ++------------
> >  1 file changed, 2 insertions(+), 12 deletions(-)
> 
> Hi Mauro,
> 
> I'm writing for just a gentle ping for this and two other staging/
atomisp/ 
> patches that still seem to be waiting to be applied.
> 
> In the meantime I would like to remind you that Hans de Goede has 
> successfully tested this patch and the other two on both the front and 
back 
> cams of a chuwi hi8 tablet.

Hi Mauro,

In my previous message I forgot to remind you that two of these three 
patches have also been reviewed by Ira Weiny (Intel).

I'd like to ask you again if there is still something left which prevents 
these three patches from being accepted. The first of the three patches was 
submitted on April 9, 2022.

For you convenience here are the links to the patches, the "Reviewed-by:" 
and "Tested-by:" tags:

[PATCH] staging: media: atomisp: Use kmap_local_page() in hmm_store()
https://lore.kernel.org/lkml/20220413225531.9425-1-fmdefrancesco@gmail.com/
https://lore.kernel.org/lkml/Yli+R7iLZKqO8kVP@iweiny-desk3/
https://lore.kernel.org/lkml/2d096f20-dbaa-1d49-96e9-a7ae6c19f7fe@redhat.com/

[PATCH] staging: media: atomisp: Use kmap_local_page() in hmm_set()
https://lore.kernel.org/lkml/20220413212210.18494-1-fmdefrancesco@gmail.com/
https://lore.kernel.org/lkml/YldNhErgt53RqYp7@iweiny-desk3/
https://lore.kernel.org/lkml/0b04ad1a-e442-1728-ef2c-bab386a4c64c@redhat.com/

[PATCH] staging: media: atomisp: Convert kmap() to kmap_local_page()
https://lore.kernel.org/lkml/20220408223129.3844-1-fmdefrancesco@gmail.com/
https://lore.kernel.org/lkml/b0aed731-b56f-4378-b50e-fc0cbccbdb84@redhat.com/

Thanks,

Fabio M. De Francesco

P.S.: Do you want me to resend them all and add the above-mentioned tags?