linux-kernel - Re: [PATCH] platform/chrome: cros_ec_lpc: Fix error code in cros_ec_lpc_mec_read

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Message-ID: <ZmsvHBrYSpwYLyxx@google.com>
Date: Thu, 13 Jun 2024 17:40:44 +0000
From: Tzung-Bi Shih <tzungbi@...nel.org>
To: Ben Walsh <ben@...nut.com>
Cc: Dan Carpenter <dan.carpenter@...aro.org>,
	Benson Leung <bleung@...omium.org>,
	Guenter Roeck <groeck@...omium.org>,
	chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] platform/chrome: cros_ec_lpc: Fix error code in
 cros_ec_lpc_mec_read_bytes()

On Thu, Jun 13, 2024 at 05:51:39PM +0100, Ben Walsh wrote:
> 
> Thanks for fixing this! Unfortunately `in_range` returns -EINVAL if
> length == 0 (see the definition of `fwk_ec_lpc_mec_in_range`). I'm sure
> this broke something in my testing, but I can't find what it was now.

Somewhere like [1] could accidentally get the -EINVAL.

[1]: https://elixir.bootlin.com/linux/v6.9/source/drivers/platform/chrome/cros_ec_lpc.c#L232
> 
> My original suggestion was to add a test for "length == 0" before the
> "in_range" test, then do the test as you have done. But we decided to
> defer this to a later, separate patch.
> 
> There's also a similar "in_range" test in `fwk_ec_lpc_mec_write_bytes`.
> 
> We could:
> 
>   1. Revert this and change the `data & EC_LPC_STATUS_BUSY_MASK` to
>   `res & EC_LPC_STATUS_BUSY_MASK`. This is the same logic as before the
>   negative error code change.
> 
>   or 2. Put in a check for length == 0.
> 
>   or 3. Change the logic in `fwk_ec_lpc_mec_in_range`. Although I'm not
>   sure what the correct answer is to "zero length is in range?"
> 
> I prefer option 2. What do you think?

How about drop the length check at [2]?

[2]: https://elixir.bootlin.com/linux/v6.9/source/drivers/platform/chrome/cros_ec_lpc_mec.c#L44

> 
> Dan Carpenter <dan.carpenter@...aro.org> writes:
> 
> > We changed these functions to returning negative error codes, but this
> > first error path was accidentally overlooked.  It leads to a Smatch
> > warning:
> >
> >     drivers/platform/chrome/cros_ec_lpc.c:181 ec_response_timed_out()
> >     error: uninitialized symbol 'data'.
> >
> > Fix this by returning the error code instead of success.
> >
> > Fixes: 68dbac0a58ef ("platform/chrome: cros_ec_lpc: MEC access can return error code")
> > Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> > ---
> >  drivers/platform/chrome/cros_ec_lpc.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/platform/chrome/cros_ec_lpc.c b/drivers/platform/chrome/cros_ec_lpc.c
> > index ebe9fb143840..f0470248b109 100644
> > --- a/drivers/platform/chrome/cros_ec_lpc.c
> > +++ b/drivers/platform/chrome/cros_ec_lpc.c
> > @@ -139,7 +139,7 @@ static int cros_ec_lpc_mec_read_bytes(unsigned int offset, unsigned int length,
> >  	int in_range = cros_ec_lpc_mec_in_range(offset, length);
> >  
> >  	if (in_range < 0)
> > -		return 0;
> > +		return in_range;
> >  
> >  	return in_range ?
> >  		cros_ec_lpc_io_bytes_mec(MEC_IO_READ,
> > @@ -158,7 +158,7 @@ static int cros_ec_lpc_mec_write_bytes(unsigned int offset, unsigned int length,
> >  	int in_range = cros_ec_lpc_mec_in_range(offset, length);
> >  
> >  	if (in_range < 0)
> > -		return 0;
> > +		return in_range;
> >  
> >  	return in_range ?
> >  		cros_ec_lpc_io_bytes_mec(MEC_IO_WRITE,
> > -- 
> > 2.43.0
>