From: Bjorn Andersson <bjorn.andersson@linaro.org> To: Doug Anderson <dianders@chromium.org> Cc: David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>, Rob Herring <robh+dt@kernel.org>, Andrzej Hajda <a.hajda@samsung.com>, Neil Armstrong <narmstrong@baylibre.com>, Laurent Pinchart <Laurent.pinchart@ideasonboard.com>, Jonas Karlman <jonas@kwiboo.se>, Jernej Skrabec <jernej.skrabec@siol.net>, dri-devel <dri-devel@lists.freedesktop.org>, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" <devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, linux-arm-msm <linux-arm-msm@vger.kernel.org> Subject: Re: [PATCH 1/2] dt-bindings: drm/bridge: ti-sn65dsi86: Replace #pwm-cells Date: Mon, 2 Nov 2020 11:08:01 -0600 [thread overview] Message-ID: <20201102170801.GI3151@builder.lan> (raw) In-Reply-To: <CAD=FV=Unu-PH_RThi3xRF1HUADN2PqcVAOin0O0yo0gcGRWCDQ@mail.gmail.com> On Fri 02 Oct 15:42 CDT 2020, Doug Anderson wrote: > Hi, > > On Wed, Sep 30, 2020 at 3:40 PM Bjorn Andersson > <bjorn.andersson@linaro.org> wrote: > > > > While the signal on GPIO4 to drive the backlight controller indeed is > > pulse width modulated its purpose is specifically to control the > > brightness of a backlight. > > I'm a bit on the fence about this. I guess you're doing this because > it avoids some -EPROBE_DEFER cycles in Linux? It does seem to have a > few downsides, though. > No, the reason for exposing a backlight is that while the thing certainly is a PWM signal, the description of it and the registers available to control it surely seems "backlight" to me. In particular No, the reason for exposing a backlight is that while while the thing certainly is a PWM signal, the description of it and the registers available to control it surely seems "backlight" to me. > 1. It means a bit of re-inventing the wheel. It's not a very big > wheel, though, I'll give you. ...but it's still something. > The main problem I saw with exposing this as a PWM was the fact that we have both period and frequency to control... > 2. I'm not sure why you'd want to, but in theory one could use this > PWM for some other purposes. It really is just a generic PWM. Your > change prevents that. > ...and in the even that you use it as a "generic" PWM I'd expect that the specified period is related to the frequency of the signal. But the period is documented to be related to the number of brightness steps of the panel. > > > > Drop the #pwm-cells and instead expose a new property to configure the > > granularity of the backlight PWM signal. > > > > Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org> > > --- > > .../devicetree/bindings/display/bridge/ti,sn65dsi86.yaml | 9 ++++++--- > > 1 file changed, 6 insertions(+), 3 deletions(-) > > > > diff --git a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > > index f8622bd0f61e..e380218b4646 100644 > > --- a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > > +++ b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > > @@ -66,9 +66,12 @@ properties: > > 1-based to match the datasheet. See ../../gpio/gpio.txt for more > > information. > > > > - '#pwm-cells': > > - const: 1 > > - description: See ../../pwm/pwm.yaml for description of the cell formats. > > + ti,backlight-scale: > > + description: > > + The granularity of brightness for the PWM signal provided on GPIO4, if > > + this property is specified. > > + minimum: 0 > > + maximum: 65535 > > A few issues here: > > 1. Maybe call this "num-steps" instead of backlight-scale. That's > essentially what it is, right? Saying how many discrete steps you're > allowing in your backlight? > That would work, I had it as "max-brightness" for a while as well. But I reverted to backlight-scale, because that's the name used in the datasheet. I'm fine with whatever color of the shed though :) > 2. IMO you need the PWM frequency specified, since it can actually > matter. NOTE: once you have the PWM frequency specified, you could > imagine automatically figuring out what "num-steps" was. Really you'd > want it to be the largest possible value you could achieve with your > hardware at the specified frequency. There's no advantage (is there?) > of providing fewer steps to the backlight client. > I guess there's no problem in having a "num-steps" that is unrelated to the number of brightness steps of the panel - but I did distinguish them because the datasheet clearly does so. > 3. Some backlights are specified inverted. It looks like this maps > nicely to the bridge chip, which has a bit for it. Probably nice to > expose this? > Yes, that should be covered. > Of course, if we were just exposing the PWM directly to Linux we could > just use the PWM backlight driver and it'd all magically work. ;-) > Please help me figure out how to properly expose this in the PWM api and I'll be happy to respin it using this - as you say my wheel does look pretty similar... Regards, Bjorn
WARNING: multiple messages have this Message-ID (diff)
From: Bjorn Andersson <bjorn.andersson@linaro.org> To: Doug Anderson <dianders@chromium.org> Cc: "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" <devicetree@vger.kernel.org>, Jernej Skrabec <jernej.skrabec@siol.net>, Neil Armstrong <narmstrong@baylibre.com>, David Airlie <airlied@linux.ie>, linux-arm-msm <linux-arm-msm@vger.kernel.org>, Jonas Karlman <jonas@kwiboo.se>, LKML <linux-kernel@vger.kernel.org>, dri-devel <dri-devel@lists.freedesktop.org>, Andrzej Hajda <a.hajda@samsung.com>, Rob Herring <robh+dt@kernel.org>, Laurent Pinchart <Laurent.pinchart@ideasonboard.com> Subject: Re: [PATCH 1/2] dt-bindings: drm/bridge: ti-sn65dsi86: Replace #pwm-cells Date: Mon, 2 Nov 2020 11:08:01 -0600 [thread overview] Message-ID: <20201102170801.GI3151@builder.lan> (raw) In-Reply-To: <CAD=FV=Unu-PH_RThi3xRF1HUADN2PqcVAOin0O0yo0gcGRWCDQ@mail.gmail.com> On Fri 02 Oct 15:42 CDT 2020, Doug Anderson wrote: > Hi, > > On Wed, Sep 30, 2020 at 3:40 PM Bjorn Andersson > <bjorn.andersson@linaro.org> wrote: > > > > While the signal on GPIO4 to drive the backlight controller indeed is > > pulse width modulated its purpose is specifically to control the > > brightness of a backlight. > > I'm a bit on the fence about this. I guess you're doing this because > it avoids some -EPROBE_DEFER cycles in Linux? It does seem to have a > few downsides, though. > No, the reason for exposing a backlight is that while the thing certainly is a PWM signal, the description of it and the registers available to control it surely seems "backlight" to me. In particular No, the reason for exposing a backlight is that while while the thing certainly is a PWM signal, the description of it and the registers available to control it surely seems "backlight" to me. > 1. It means a bit of re-inventing the wheel. It's not a very big > wheel, though, I'll give you. ...but it's still something. > The main problem I saw with exposing this as a PWM was the fact that we have both period and frequency to control... > 2. I'm not sure why you'd want to, but in theory one could use this > PWM for some other purposes. It really is just a generic PWM. Your > change prevents that. > ...and in the even that you use it as a "generic" PWM I'd expect that the specified period is related to the frequency of the signal. But the period is documented to be related to the number of brightness steps of the panel. > > > > Drop the #pwm-cells and instead expose a new property to configure the > > granularity of the backlight PWM signal. > > > > Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org> > > --- > > .../devicetree/bindings/display/bridge/ti,sn65dsi86.yaml | 9 ++++++--- > > 1 file changed, 6 insertions(+), 3 deletions(-) > > > > diff --git a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > > index f8622bd0f61e..e380218b4646 100644 > > --- a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > > +++ b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > > @@ -66,9 +66,12 @@ properties: > > 1-based to match the datasheet. See ../../gpio/gpio.txt for more > > information. > > > > - '#pwm-cells': > > - const: 1 > > - description: See ../../pwm/pwm.yaml for description of the cell formats. > > + ti,backlight-scale: > > + description: > > + The granularity of brightness for the PWM signal provided on GPIO4, if > > + this property is specified. > > + minimum: 0 > > + maximum: 65535 > > A few issues here: > > 1. Maybe call this "num-steps" instead of backlight-scale. That's > essentially what it is, right? Saying how many discrete steps you're > allowing in your backlight? > That would work, I had it as "max-brightness" for a while as well. But I reverted to backlight-scale, because that's the name used in the datasheet. I'm fine with whatever color of the shed though :) > 2. IMO you need the PWM frequency specified, since it can actually > matter. NOTE: once you have the PWM frequency specified, you could > imagine automatically figuring out what "num-steps" was. Really you'd > want it to be the largest possible value you could achieve with your > hardware at the specified frequency. There's no advantage (is there?) > of providing fewer steps to the backlight client. > I guess there's no problem in having a "num-steps" that is unrelated to the number of brightness steps of the panel - but I did distinguish them because the datasheet clearly does so. > 3. Some backlights are specified inverted. It looks like this maps > nicely to the bridge chip, which has a bit for it. Probably nice to > expose this? > Yes, that should be covered. > Of course, if we were just exposing the PWM directly to Linux we could > just use the PWM backlight driver and it'd all magically work. ;-) > Please help me figure out how to properly expose this in the PWM api and I'll be happy to respin it using this - as you say my wheel does look pretty similar... Regards, Bjorn _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
next prev parent reply other threads:[~2020-11-02 17:08 UTC|newest] Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-09-30 22:35 [PATCH 0/2] drm/bridge: ti-sn65dsi86: Support backlight controls Bjorn Andersson 2020-09-30 22:35 ` Bjorn Andersson 2020-09-30 22:35 ` [PATCH 1/2] dt-bindings: drm/bridge: ti-sn65dsi86: Replace #pwm-cells Bjorn Andersson 2020-09-30 22:35 ` Bjorn Andersson 2020-09-30 23:06 ` Steev Klimaszewski 2020-09-30 23:06 ` Steev Klimaszewski 2020-10-02 20:42 ` Doug Anderson 2020-10-02 20:42 ` Doug Anderson 2020-11-02 17:08 ` Bjorn Andersson [this message] 2020-11-02 17:08 ` Bjorn Andersson 2020-11-11 0:48 ` Doug Anderson 2020-11-11 0:48 ` Doug Anderson 2020-10-05 13:50 ` Rob Herring 2020-10-05 13:50 ` Rob Herring 2020-09-30 22:35 ` [PATCH 2/2] drm/bridge: ti-sn65dsi86: Expose backlight controls Bjorn Andersson 2020-09-30 22:35 ` Bjorn Andersson 2020-09-30 23:07 ` Steev Klimaszewski 2020-09-30 23:07 ` Steev Klimaszewski 2020-10-02 20:42 ` Doug Anderson 2020-10-02 20:42 ` Doug Anderson
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20201102170801.GI3151@builder.lan \ --to=bjorn.andersson@linaro.org \ --cc=Laurent.pinchart@ideasonboard.com \ --cc=a.hajda@samsung.com \ --cc=airlied@linux.ie \ --cc=daniel@ffwll.ch \ --cc=devicetree@vger.kernel.org \ --cc=dianders@chromium.org \ --cc=dri-devel@lists.freedesktop.org \ --cc=jernej.skrabec@siol.net \ --cc=jonas@kwiboo.se \ --cc=linux-arm-msm@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=narmstrong@baylibre.com \ --cc=robh+dt@kernel.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.