linux-kernel - Re: [PATCH 2/2] power: supply: Add Lenovo Yoga C630 EC driver

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Date:   Fri, 16 Sep 2022 00:53:42 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Bjorn Andersson <andersson@...nel.org>
Cc:     Sebastian Reichel <sebastian.reichel@...labora.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Lee Jones <lee@...nel.org>, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 2/2] power: supply: Add Lenovo Yoga C630 EC driver

On Fri, 16 Sept 2022 at 00:25, Bjorn Andersson <andersson@...nel.org> wrote:
>
> On Tue, Sep 13, 2022 at 12:45:45PM +0200, Sebastian Reichel wrote:
> > Hi,
> >
> > [+Cc Lee Jones, DRI devel]
> >
> > On Tue, Aug 09, 2022 at 10:05:00PM -0500, Bjorn Andersson wrote:
> > > The Qualcomm Snapdragon-based Lenovo Yoga C630 has some sort of EC
> > > providing AC-adapter and battery status, as well as USB Type-C altmode
> > > notifications for Displayport operation.
> > >
> > > The Yoga C630 ships with Windows, where these operations primarily are
> > > implemented in ACPI, but due to various issues with the hardware
> > > representation therein it's not possible to run Linux on this
> > > information. As such this is a best-effort re-implementation of these
> > > operations, based on the register map expressed in ACPI and a fair
> > > amount of trial and error.
> > >
> > > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > > ---
> > > [...]
> > > +   val = yoga_c630_ec_read8(ec, LENOVO_EC_BAT_ATTRIBUTES);
> > > +   if (val < 0)
> > > +           goto out_unlock;
> > > +   ec->unit_ma = val & LENOVO_EC_BAT_ATTR_UNIT_IS_MA;
> > > +   if (!ec->unit_ma)
> > > +           ec->scale = 1000;
> > > +   else
> > > +           ec->scale = 1;
> >
> > Since I'm not sure how much of information was gained by reverse
> > engineering: Is this really milliamps vs microamps and not milliamps
> > vs milliwatt? SBS batteries usually report either mA or mW.
> >
>
> Unfortunately I don't know the answer to this.
>
> > > [...]
> > > +   case POWER_SUPPLY_PROP_SERIAL_NUMBER:
> > > +           val->strval = "05072018";
> > > +           break;
> >
> > why is this hardcoded? :)
> >
>
> I don't know, but as Daniel suggests, it would make sense to just drop
> it.
>
> > > [...]
> > > +   device_for_each_child_node(dev, fwnode) {
> > > +           ret = fwnode_property_read_u32(fwnode, "reg", &port);
> > > +           if (ret < 0)
> > > +                   continue;
> > > +
> > > +           /* Got multiple ports, but altmode is only possible on port 1 */
> > > +           if (port != 1)
> > > +                   continue;
> > > +
> > > +           ec->bridge.funcs = &yoga_c630_ec_bridge_funcs;
> > > +           ec->bridge.of_node = to_of_node(fwnode);
> > > +           ec->bridge.ops = DRM_BRIDGE_OP_HPD;
> > > +           ec->bridge.type = DRM_MODE_CONNECTOR_USB;
> > > +
> > > +           ret = devm_drm_bridge_add(dev, &ec->bridge);
> > > +           if (ret) {
> > > +                   dev_err(dev, "failed to register drm bridge\n");
> > > +                   fwnode_handle_put(fwnode);
> > > +                   return ret;
> > > +           }
> >
> > I wonder if DRM people want to see this in drivers/gpu/drm/bridge.
> > Maybe it's better to make this a MFD driver?
> >
>
> I did consider it, but it adds a whole bunch of boiler plate code
> without a lot of benefit.
>
> There are a few other cases where I think it would make sense to have
> drm bridges outside of drivers/gpu/drm, such as
> drivers/usb/typec/altmodes/ and drivers/platform/chrome/...

What about a solution which might sound simpler than MFD: from your
driver's probe() register a platform device which represents a drm
bridge. Add drm_bridge driver for it into drivers/gpu/drm/bridges/.



-- 
With best wishes
Dmitry