Re: [PATCH] media: v4l: cadence: Fix how unsued lanes are handled in 'csi2rx_start()'

[Christophe JAILLET]

Le 16/09/2019 Ã 08:28, Dan Carpenter a ÃcritÂ:
> 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@xxxxxxxxxx>
> > > ---
> > > 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.

Hi Dan,

not sure to follow you.

csi2rx_probe()
 --> csi2rx_get_resources()
 Â --> ...
ÂÂÂ ÂÂÂÂÂ dev_cfg = readl(csi2rx->base + CSI2RX_DEVICE_CFG_REG);
ÂÂÂ ÂÂÂ Â ...
ÂÂÂ ÂÂÂÂÂ csi2rx->max_lanes = dev_cfg & 7;
ÂÂÂÂÂÂÂÂÂ if (csi2rx->max_lanes > CSI2RX_LANES_MAX) {
ÂÂÂ ÂÂ Â Â Â dev_err(&pdev->dev, "Invalid number of lanes: %u\n",
ÂÂÂ ÂÂÂ ÂÂ Â Â Â Â Â csi2rx->max_lanes);
   Â Â return -EINVAL;
ÂÂÂÂÂÂÂÂÂ }

So I guess, that we can trust max_lanes because of the 'if (... > 
CSI2RX_LANES_MAX)' check.

Did I miss something?


> 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