Re: [PATCH 7/7] platform/chrome: cros_ec_lightbar: instantiate only if the EC has a lightbar.

[Guenter Roeck]

On 11/23/18 3:10 AM, Enric Balletbo i Serra wrote:
> Hi Guenter,
>
> On 22/11/18 20:25, Guenter Roeck wrote:
> > On Thu, Nov 22, 2018 at 12:33:56PM +0100, Enric Balletbo i Serra wrote:
> > > Due to the way attribute groups visibility work, the function
> > > cros_ec_lightbar_attrs_are_visible is called multiple times, once per
> > > attribute, and each of these calls makes an EC transaction. For what is
> > > worth the EC log reports multiple errors on boot when the lightbar is
> > > not available. Instead, check if the EC has a lightbar in the probe
> > > function and only instantiate the device.
> > >
> > > Ideally we should have instantiate the driver only if the
> > > EC_FEATURE_LIGHTBAR is defined, but that's not possible because that flag
> > > is not in the very first Pixel Chromebook (Link), only on Samus. So, the
> > > driver is instantiated by his parent always.
> > >
> > > This patch changes a bit the actual behaviour. Before the patch if an EC
> > > doesn't have a lightbar an empty lightbar folder is created in
> > > /sys/class/chromeos/<ec device>, after the patch the empty folder is not
> > > created, so, the folder is only created if the lightbar exists.
> > >
> > > Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
> >
> > Guess this is the answer to the suggestion I had before. Maybe the two patches
> > should be merged together ? Or do  others think that they should be kept
> > separate ?
>
> I did in a separate patch because it changes a bit the current behaviour (i.e
> after that patch the lightbar directory will not appear if is not detected).
> Having in a separate patch will allow us to revert cleanly if for some weird
> reason we still want the old behaviour. So in general, first I moved the
> attributes and then I did a follow up patch with the probe change. This also
> happens with vbc driver.

Good point, makes sense.

> Said that, I don't mind to merge the two patches.
>
>
> > Additional comment below.
> >
> > Thanks,
> > Guenter
> >
> > > ---
> > >
> > >   drivers/platform/chrome/cros_ec_lightbar.c | 29 +++++++++-------------
> > >   1 file changed, 12 insertions(+), 17 deletions(-)
> > >
> > > diff --git a/drivers/platform/chrome/cros_ec_lightbar.c b/drivers/platform/chrome/cros_ec_lightbar.c
> > > index 31d22f594fac..d255264eb082 100644
> > > --- a/drivers/platform/chrome/cros_ec_lightbar.c
> > > +++ b/drivers/platform/chrome/cros_ec_lightbar.c
> > > @@ -567,37 +567,28 @@ static struct attribute *__lb_cmds_attrs[] = {
> > >   	NULL,
> > >   };
> > >   
> > > -static bool ec_has_lightbar(struct cros_ec_dev *ec)
> > > +static bool cros_ec_has_lightbar(struct cros_ec_dev *ec_dev)
> > >   {
> > > -	return !!get_lightbar_version(ec, NULL, NULL);
> > > -}
> > > -
> > > -static umode_t cros_ec_lightbar_attrs_are_visible(struct kobject *kobj,
> > > -						  struct attribute *a, int n)
> > > -{
> > > -	struct device *dev = container_of(kobj, struct device, kobj);
> > > -	struct cros_ec_dev *ec = to_cros_ec_dev(dev);
> > > -	struct platform_device *pdev = to_platform_device(ec->dev);
> > > +	struct platform_device *pdev = to_platform_device(ec_dev->dev);
> > >   	struct cros_ec_platform *pdata = pdev->dev.platform_data;
> > >   	int is_cros_ec;
> > >   
> > >   	is_cros_ec = strcmp(pdata->ec_name, CROS_EC_DEV_NAME);
> > >   
> > Can this now ever be false ?
>
> Yes, this happens for example on Samus, where there are two ECs, the first one
> is named "cros_ec" and the second one is "cros_pd", so will fail in the second
> case. Gwendal, correct me if I am wrong, but AFAIK this is a bit of hack because
> some initial versions of Samus (coded Link I guess) have no support for the
> EC_LIGHTBAR_FEATURE so we can't really use the features thing.
Ok.

Thanks,
Guenter

> > >   	if (is_cros_ec != 0)
> > > -		return 0;
> > > +		return false;
> > >   
> > > -	/* Only instantiate this stuff if the EC has a lightbar */
> > > -	if (ec_has_lightbar(ec)) {
> > > -		ec_with_lightbar = ec;
> > > -		return a->mode;
> > > +	if (!!get_lightbar_version(ec_dev, NULL, NULL)) {
> > > +		ec_with_lightbar = ec_dev;
> >
> > Is this variable (and the associated check in lb_manual_suspend_ctrl)
> > still necessary ?
>
> Hmm, right, I will double check and remove in next version.
>
> > > +		return true;
> > >   	}
> > > -	return 0;
> > > +
> > > +	return false;
> > >   }
> > >   
> > >   struct attribute_group cros_ec_lightbar_attr_group = {
> > >   	.name = "lightbar",
> > >   	.attrs = __lb_cmds_attrs,
> > > -	.is_visible = cros_ec_lightbar_attrs_are_visible,
> > >   };
> > >   
> > >   static int cros_ec_lightbar_probe(struct platform_device *pd)
> > > @@ -611,6 +602,10 @@ static int cros_ec_lightbar_probe(struct platform_device *pd)
> > >   		return -EINVAL;
> > >   	}
> > >   
> > > +	/* Only instantiate this stuff if the EC has a lightbar */
> > > +	if (!cros_ec_has_lightbar(ec_dev))
> > > +		return -ENODEV;
> > > +
> > >   	/* Take control of the lightbar from the EC. */
> > >   	lb_manual_suspend_ctrl(ec_dev, 1);
> > >