From: Pavel Machek <firstname.lastname@example.org> To: Bjorn Andersson <email@example.com> Cc: Dan Murphy <firstname.lastname@example.org>, Rob Herring <email@example.com>, Andy Gross <firstname.lastname@example.org>, Thierry Reding <email@example.com>, Uwe Kleine-K?nig <firstname.lastname@example.org>, Lee Jones <email@example.com>, Martin Botka <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [PATCH v6 2/4] leds: Add driver for Qualcomm LPG Date: Tue, 4 May 2021 17:43:05 +0200 [thread overview] Message-ID: <YJFridMwwMV1K98m@mobian> (raw) In-Reply-To: <20210429212920.GB2484@yoga> Hi! > > > One such example is the laptop in front of me, which has 3 channels > > > wired to an RGB LED and 1 channel wired as a backlight control signal > > > (i.e. using pwm-backlight). Another example is a devboard where the > > > 4 channels are wired to 4 LEDs. > > > > Ok, so this is actually important. In this case you should have PWM > > layer, exporting PWMs, and then rgb-LED driver that takes three of > > those PWMs and turns them into LED, no? > > > > And ... surprise ... that is likely to help other people, as LEDs > > connected to PWMs are quite common. > > > > Hmm.? > > > > If you can't do this for some reason, you should probably explain in > > the changelog, because this is going to be FAQ. > > > > This is exactly what the downstream implementation does and in the case > of a solid color LED this works fine. > > But the hardware has a shared chunk of memory where you can write > duty-cycle values, then for each PWM channel you can specify the > start/stop index and pace for the PWM to read and update the configured > duty-cycle. This is how the hardware implements pattern support. Ok. > So downstream they have (last time I looked at the code) an addition in > the PWM API where the LED driver can inform the PWM driver part about > the indices to use. Naturally I don't think that's a good idea. Dunno. Is it bad idea? pattern support for other PWMs (vibration?) seems useful, too. Yes, it means more discussion and extending PWMs properly.. > Additionally, representing this as individual PWM channels means we're > loosing the grouping that now comes from the description of multicolor > LEDs, which serves the basis for synchronizing the pattern traversal > between the involved channels. Yes, keeping grouping would be nice, but perhaps pattern API for PWMs can do that too? You can have solid-color-only driver now, with patterns being added as discussion with PWM people progresses... Best regards, Pavel --
next prev parent reply other threads:[~2021-05-04 15:43 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-10-21 20:12 [PATCH v6 0/4] Qualcomm Light Pulse Generator Bjorn Andersson 2020-10-21 20:12 ` [PATCH v6 1/4] dt-bindings: leds: Add Qualcomm Light Pulse Generator binding Bjorn Andersson 2020-10-26 15:02 ` Rob Herring 2020-10-21 20:12 ` [PATCH v6 2/4] leds: Add driver for Qualcomm LPG Bjorn Andersson 2020-10-22 19:25 ` Luca Weiss 2020-10-29 18:13 ` Pavel Machek 2021-04-29 0:12 ` Bjorn Andersson 2021-04-29 21:12 ` Pavel Machek 2021-04-29 21:29 ` Bjorn Andersson 2021-05-04 15:43 ` Pavel Machek [this message] 2021-05-04 16:13 ` Bjorn Andersson 2021-05-05 5:21 ` Uwe Kleine-König 2021-04-18 21:54 ` Marijn Suijten 2021-04-28 22:39 ` Bjorn Andersson 2021-04-29 19:31 ` Marijn Suijten 2021-04-29 20:54 ` Bjorn Andersson 2021-05-05 5:15 ` Uwe Kleine-König 2021-05-05 5:19 ` Uwe Kleine-König 2021-05-13 17:43 ` Bjorn Andersson 2020-10-21 20:12 ` [PATCH v6 3/4] arm64: dts: qcom: pm(i)8994: Add mpp and lpg blocks Bjorn Andersson 2020-10-21 20:12 ` [PATCH v6 4/4] arm64: dts: qcom: Add user LEDs on db820c Bjorn Andersson 2021-04-15 10:46 [PATCH v6 2/4] leds: Add driver for Qualcomm LPG Yassine Oudjana
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