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

Enric Balletbo i Serra
2018-11-23T11:10:22Z

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@collabora.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.

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.

>> 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);
>>
>