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

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Date:   Thu, 22 Nov 2018 11:25:44 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc:     lee.jones@...aro.org, gwendal@...omium.org, drinkcat@...omium.org,
        linux-kernel@...r.kernel.org, groeck@...omium.org,
        kernel@...labora.com, bleung@...omium.org,
        Olof Johansson <olof@...om.net>
Subject: Re: [PATCH 7/7] platform/chrome: cros_ec_lightbar: instantiate only
 if the EC has a lightbar.

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@...labora.com>

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 ?

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 ?

>  	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 ?

> +		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);
>