From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jacek Anaszewski Subject: Re: [PATCH v2 1/2] leds: Add Intel Cherry Trail Whiskey Cove PMIC LEDs Date: Thu, 14 Feb 2019 22:46:42 +0100 Message-ID: <2b6faaa5-b21e-a512-de7d-ca21be5045fc@gmail.com> References: <20190212205901.13037-1-jekhor@gmail.com> <20190212205901.13037-2-jekhor@gmail.com> <1df39a63-533f-bb68-a056-a0241f148be9@redhat.com> <20190213230731.GA8557@amd> <42078a81-e32e-81b7-528f-d1adb60d31c3@redhat.com> <20190213233806.GA11867@amd> <562e2acd-a60a-2aea-4050-6d9414d23a4e@redhat.com> <20190214111423.GE6132@amd> <92cf09b8-726d-4f1b-94ba-368a66af2246@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <92cf09b8-726d-4f1b-94ba-368a66af2246@redhat.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Hans de Goede , Pavel Machek Cc: Yauhen Kharuzhy , linux-kernel@vger.kernel.org, linux-leds@vger.kernel.org List-Id: linux-leds@vger.kernel.org Hi Hans and all, On 2/14/19 12:31 PM, Hans de Goede wrote: > Hi, > > On 14-02-19 12:14, Pavel Machek wrote: >> Hi! > > > >>> That assumes that breathing is the default setting on all hardware >>> and again I don't see why not to export this functionality to > > >> Save the status on boot, then restore it on rmmod/reboot/poweroff? :-). > > Which works until the system freezes one time. I believe that > if we are going to do a LED driver for the charging LED on these > devices, we MUST offer a way to put it back in its original > state, even if the state is foo-barred at bootup. > >>> userspace. Just because something does not fit in the existing >>> API is IMHO not a good reason to not expose it to userspace. >>> >>> I suggest that we deal with this special case by adding 3 custom >>> sysfs attributes: >>> >>> 1) "mode" which when read, prints, e.g. : >>> manual [on-when-charging] >> >> While this allows _user on console_ to control everything using echo, >> it is not suitable for applications trying to control LEDs. >> >> As there's nothing special about the case here, I believe we should >> have generic solution here. >> >> My preffered solution would be "hardware" trigger that leaves the LED >> in hardware control. > > As you explained in the parts which I snipped, there are many > devices which have a similar choice for a LED being under hw or > user control. I can see how this looks like a trigger and how we > could use the trigger API for this. > > I believe though, that if we implement a "virtual" (for lack of > a better word) trigger for this, that this should be done in the > LED core. I can envision this working like this: > > 1) Add a: > > hw_control_set(struct led_classdev *led_cdev, bool enable_hw_control); Please note that we have support for hw patterns in the pattern trigger. (see how drivers/leds/leds-sc27xx-bltc.c makes use of it for its breathing pattern). We have also support for hw blinking in timer trigger via blink_set op. In addition to that there is brightness_hw_changed sysfs attribute with led_classdev_notify_brightness_hw_changed() LED API. Couldn't they be used in concert to support the specific features of the device in question? > > Callback to struct led_classdev which when implemented by a driver > like the current PMIC LED controller would do what it says. > > 2) Have the core create and register a virtual hardware trigger the > first time a LED cdev which has this callback gets registered. > > When configured as the trigger for this LED device this trigger calls > hw_control_set(cdev, true) and when unregistered calls > hw_control_set(cdev, false) > > Taking a quick look at the trigger code, a problem with this is > that normally any trigger can work with any led device, so this > "hardware" trigger will show up in the list of possible > triggers for each device. > > This problem can be solved by making the activate method for the > hardware trigger check the classdev has a hw_control_set callback > and if not return -EINVAL, or maybe -ENXIO but still this is somewhat > inconsistent with other triggers, which AFAIK work with any LED. > >> Alternatively I could imagine "hardware" sysfs attribute, containing >> 0/1, with 0==software controlled, 1==hardware controlled. > > Hmm, maybe call it "hardware_controlled" instead ? Otherwise this > would work for me and I would personally prefer this solution. This > could even be done in the LED core using the hw_control_set callback > I proposed, to make sure it is handled consistently between devices. > >> The rest of attributes would have to be Cove-specific, yes (but still >> should fit with the rest of LED subsystem). > > Right, I see that the triggers attribute already uses the fmt where > on "cat" all options are listed and the current active one has [] around > it, > so I think the pattern and frequency attributes I proposed should work > well, although thinking more about this I believe the freq. attribute > should > be called pattern_freq to make clear it applies to blinking / breathing > set through the pattern attribute. > > Regards, > > Hans > -- Best regards, Jacek Anaszewski