linux-kernel - Re: [PATCH] media: v4l: cadence: Fix how unsued lanes are handled in 'csi2rx

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Message-ID: <20190916062846.GD18977@kadam>
Date:   Mon, 16 Sep 2019 09:28:46 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Maxime Ripard <mripard@...nel.org>
Cc:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        mchehab@...nel.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] media: v4l: cadence: Fix how unsued lanes are handled in
 'csi2rx_start()'

On Fri, Sep 13, 2019 at 09:57:09AM +0200, Maxime Ripard wrote:
> Hi Christophe,
> 
> On Thu, Sep 12, 2019 at 10:44:50PM +0200, Christophe JAILLET wrote:
> > The 2nd parameter of 'find_first_zero_bit()' is a number of bits, not of
> > bytes. So use 'BITS_PER_LONG' instead of 'sizeof(lanes_used)'.
> > 
> > Fixes: 1fc3b37f34f6 ("media: v4l: cadence: Add Cadence MIPI-CSI2 RX driver")
> > Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> > ---
> > This patch is purely speculative. Using BITS_PER_LONG looks logical to me,
> > but I'm not 100% sure that it is what is expected here. 'csi2rx->max_lanes'
> > could also be a good candidate.
> 
> Yeah, csi2rx->max_lanes would make more sense in that context. Could
> you resend a new version?

This is sort of unrelated, but for Smatch purposes the csi2rx->max_lanes
comes from the firmware in csi2rx_parse_dt() and it could be any u8
value.

I sort of wish that people would write code which was known to be
correct just from reading the kernel code, without looking at the
firmware...  I guess I could mark v4l2_fwnode_endpoint_parse() as always
giving us valid data, but that still wouldn't tell us what the valid
data is.  It's hard to know the right answer from a static analysis
point of view.

regards,
dan carpenter