linux-kernel - Re: [PATCH] platform/chrome: cros_ec_proto: Fix check

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Date:   Tue, 21 Sep 2021 10:29:37 -0700
From:   Prashant Malani <pmalani@...omium.org>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc:     linux-kernel@...r.kernel.org, Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: Re: [PATCH] platform/chrome: cros_ec_proto: Fix check_features ret
 val

Hi Enric,

Thanks for reviewing the patch.

On Tue, Sep 21, 2021 at 01:42:04PM +0200, Enric Balletbo i Serra wrote:
> Hi Prashant,
> 
> Thank you for the patch. Just one comment below ...
> 
> On 16/9/21 3:46, Prashant Malani wrote:
> > The kerneldoc for cros_ec_check_features() states that it returns 1 or 0
> > depedending on whether a feature is supported or not, but it instead
> > returns a negative error number in one case, and a non-1 bitmask in
> > other cases.
> > 
> > Since all call-sites only check for a 1 or 0 return value, update
> > the function to return boolean values.
> > 
> > Signed-off-by: Prashant Malani <pmalani@...omium.org>
> > ---
> >  drivers/platform/chrome/cros_ec_proto.c     | 12 +++++++-----
> >  include/linux/platform_data/cros_ec_proto.h |  2 +-
> >  2 files changed, 8 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/platform/chrome/cros_ec_proto.c b/drivers/platform/chrome/cros_ec_proto.c
> > index a7404d69b2d3..a34cf58c5ef7 100644
> > --- a/drivers/platform/chrome/cros_ec_proto.c
> > +++ b/drivers/platform/chrome/cros_ec_proto.c
> > @@ -808,9 +808,9 @@ EXPORT_SYMBOL(cros_ec_get_host_event);
> >   *
> >   * Call this function to test whether the ChromeOS EC supports a feature.
> >   *
> > - * Return: 1 if supported, 0 if not
> > + * Return: true if supported, false if not (or if an error was encountered).
> >   */
> > -int cros_ec_check_features(struct cros_ec_dev *ec, int feature)
> > +bool cros_ec_check_features(struct cros_ec_dev *ec, int feature)
> >  {
> >  	struct cros_ec_command *msg;
> >  	int ret;
> > @@ -818,8 +818,10 @@ int cros_ec_check_features(struct cros_ec_dev *ec, int feature)
> >  	if (ec->features[0] == -1U && ec->features[1] == -1U) {
> >  		/* features bitmap not read yet */
> >  		msg = kzalloc(sizeof(*msg) + sizeof(ec->features), GFP_KERNEL);
> > -		if (!msg)
> > -			return -ENOMEM;
> > +		if (!msg) {
> > +			dev_err(ec->dev, "failed to allocate memory to get EC features\n");
> 
> In case of failure you will be noticed by the allocator, prints after
> [k|v][m|z|c]alloc() functions are not needed, so I think you can just return
> false here.
> > 

Makes sense; I can make the change, but I had one question:

If we solely return false, how will we tell from the logs that the
allocation error message was associated with this driver? Only returning
false means the driver probe (e.g cros-ec-typec) will continue (just assuming a certain feature
is not present). Wouldn't having this error message make this clear?

Best regards,

-Prashant