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

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Date:   Mon, 25 Apr 2022 20:29:03 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Tsuchiya Yuto <kitakar@...il.com>,
        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 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.

Please let me know if there is anything else that is required to be done in 
order to accept the three patches.

Thanks,

Fabio M. De Francesco