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

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Message-ID: <20220915212545.q6vxcnrffwr3buq2@builder.lan>
Date:   Thu, 15 Sep 2022 16:25:45 -0500
From:   Bjorn Andersson <andersson@...nel.org>
To:     Sebastian Reichel <sebastian.reichel@...labora.com>
Cc:     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 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/...

> > [...]
> 
> -- Sebastian

Thanks,
Bjorn