Re: [PATCH] ics932s401: fix broken handling of errors when word reading fails

From: Matthew Wilcox
Date: Wed Apr 28 2021 - 18:46:38 EST

On Wed, Apr 28, 2021 at 03:25:34PM -0700, Darrick J. Wong wrote:
> In commit b05ae01fdb89, someone tried to make the driver handle i2c read
> errors by simply zeroing out the register contents, but for some reason
> left unaltered the code that sets the cached register value the function
> call return value.
> The original patch was authored by a member of the Underhanded
> Mangle-happy Nerds, I'm not terribly surprised. I don't have the
> hardware anymore so I can't test this, but it seems like a pretty
> obvious API usage fix to me...

Not sure why you cc'd linux-fsdevel, but that's how i got to see it ...

> +++ b/drivers/misc/ics932s401.c
> @@ -134,7 +134,7 @@ static struct ics932s401_data *ics932s401_update_device(struct device *dev)
> for (i = 0; i < NUM_MIRRORED_REGS; i++) {
> temp = i2c_smbus_read_word_data(client, regs_to_copy[i]);
> if (temp < 0)
> - data->regs[regs_to_copy[i]] = 0;
> + temp = 0;
> data->regs[regs_to_copy[i]] = temp >> 8;
> }

Looking at a bit more context in this function, shouldn't we rather clear
'sensors_valid'? or does it really make sense to pretend we read zero
(rather than 255) from this register?

But then we'd have to actually check sensors_valid in functions like
calculate_src_freq, and i just don't know if it's worthwhile. Why not
just revert this patch?