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Message-ID: <CAAH8bW9UvDAB4NSQB6CuhBU6D=R6Ex6=5V=Ld74hYGK474_Trw@mail.gmail.com>
Date: Mon, 28 Dec 2020 12:10:46 -0800
From: Yury Norov <yury.norov@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Carsten Haitzler <carsten.haitzler@....com>,
Liviu Dudau <liviu.dudau@....com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Subject: Re: [PATCH] drm/komeda: use bitmap API to convert U32 to bitmap
On Mon, Dec 28, 2020 at 11:49 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Mon, Dec 28, 2020 at 11:43:43AM -0800, Yury Norov wrote:
> > The commit be3e477effba636ad25 ("drm/komeda: Fix bit
> > check to import to value of proper type") fixes possible
> > out-of-bound issue related to find_first_bit() usage, but
> > does not address the endianness problem.
>
> Hmm... Can you elaborate?
>
> ...
>
> > u32 comp_mask)
>
> > - unsigned long comp_mask_local = (unsigned long)comp_mask;
>
> Here we convert u32 to unsigned long (LSB is kept LSB since it happens in
> native endianess).
>
> > - id = find_first_bit(&comp_mask_local, 32);
>
> Here it takes an address to unsigned long and tries only lower 32 bits.
>
> Are you telling that find_first_bit() has an issue?
It seems you're right, there's no issue with endianness in existing code.
In fact, the line
> > - unsigned long comp_mask_local = (unsigned long)comp_mask;
is an opencoded version of bitmap_from_arr32(dst, src, 32).
Maybe it would be better to use the bitmap API here, but existing code is
correct. Sorry for the noise.
Yury
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