On Sun, Feb 02, 2014 at 06:30:00PM +0100, Jean-Francois Moine wrote:
> On Sun, 2 Feb 2014 16:20:58 +0000
> Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> 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.
The issue I'm pointing out is not whether it will be interpreted as an
error or not, it's whether the value is a correct error code. If we
don't care about the reason why an error occurs, we might as well just
return -1.
I've added my own patch which adjusts it as per above to my tree anyway,
so I'm not that worried about this.
--
FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up. Estimation
in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
Estimate before purchase was "up to 13.2Mbit".
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