On Sun, 2 Feb 2014 16:20:58 +0000
Russell King - ARM Linux <linux at arm.linux.org.uk> wrote:
> On Sat, Jan 25, 2014 at 06:14:45PM +0100, Jean-Francois Moine wrote:
> > This patch adds more error checking inn I2C I/O functions.
> > In case of I/O error, this permits to avoid writing in bad controller
> > pages, a bad chipset detection or looping when getting the EDID.
>
> I've just looked at this again, and spotted something:
>
> > -static uint8_t
> > +static int
> > reg_read(struct tda998x_priv *priv, uint16_t reg)
> > {
> > uint8_t val = 0;
> > - reg_read_range(priv, reg, &val, sizeof(val));
> > + int ret;
> > +
> > + ret = reg_read_range(priv, reg, &val, sizeof(val));
> > + if (ret < 0)
> > + return ret;
>
> So yes, this can return negative numbers.
>
> > @@ -1158,8 +1184,11 @@ tda998x_encoder_init(struct i2c_client *client,
> > tda998x_reset(priv);
> >
> > /* read version: */
> > - priv->rev = reg_read(priv, REG_VERSION_LSB) |
> > - reg_read(priv, REG_VERSION_MSB) << 8;
> > + ret = reg_read(priv, REG_VERSION_LSB) |
> > + (reg_read(priv, REG_VERSION_MSB) << 8);
> > + if (ret < 0)
> > + goto fail;
> > + priv->rev = ret;
>
> Two issues here:
>
> 1. The additional parens are /really/ not required.
> 2. What if reg_read(priv, REG_VERSION_MSB) returns a negative number?
>
> If we're going to the extent of attempting to make the read/write
> functions return errors, we should at least handle errors generated
> by them properly, otherwise it's pointless making them return errors.
>
> ret = reg_read(priv, REG_VERSION_LSB);
> if (ret < 0)
> goto fail;
>
> priv->rev = ret;
>
> ret = reg_read(priv, REG_VERSION_MSB);
> if (ret < 0)
> goto fail;
>
> priv->rev |= ret << 8;
>
> If you want it to look slightly nicer:
>
> int rev_lo, rev_hi;
>
> rev_lo = reg_read(priv, REG_VERSION_LSB);
> rev_hi = reg_read(priv, REG_VERSION_MSB);
> if (rev_lo < 0 || rev_hi < 0) {
> ret = rev_lo < 0 ? rev_lo : rev_hi;
> goto fail;
> }
>
> priv->rev = rev_lo | rev_hi << 8;
>
> I'm happy to commit such a change after this patch to clean it up, or if
> you want to regenerate your patch 2 and post /just/ that incorporating
> this change.
I think that my code works correctly: when there is an error, the
result of reg_read() is minus the error code, and this error code is
always lower than 8388607 (0x7fffff). Then, reg_read() << 8 will always
be negative.
Otherwise, I may redo a patch about the useless parenthesis.
--
Ken ar c'henta? | ** Breizh ha Linux atav! **
Jef | http://moinejf.free.fr/
