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

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Date:   Fri, 23 Nov 2018 03:39:38 -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 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@...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 ?
>>
> 
> 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);
>>>   
>>
>