linux-kernel - Re: [PATCH v3 3/5] nfc: pn533: add UART phy driver

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Date:   Mon, 29 Oct 2018 17:13:28 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Lars Poeschel <poeschel@...onage.de>
Cc:     Johan Hovold <johan@...nel.org>, devicetree@...r.kernel.org,
        Samuel Ortiz <sameo@...ux.intel.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:NFC SUBSYSTEM" <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH v3 3/5] nfc: pn533: add UART phy driver

On Mon, Oct 29, 2018 at 04:51:10PM +0100, Lars Poeschel wrote:
> On Mon, Oct 29, 2018 at 12:07:04PM +0100, Johan Hovold wrote:

> > > Wouldn't that be the scope of another later patch then ?
> > 
> > Possibly. We have accepted some serdev drivers already taking the lazy
> > approach of opening the port in probe. Depending on the driver, it may
> > not be too bad (e.g. for some specific hardware which you know you'll
> > always use), but it not really nice to have everyone pay a price in
> > terms of power-consumption for a feature that is rarely used.
> 
> Is there a way in serdev to close a port, but still occupy it ?
> I'd like to do the basic chip initialisation in _probe and then close
> the port for power-consuption reasons. I'd like to have the port still
> occupied, so that it's not available to other possible users in the
> meantime. I'd then do a serdev open again in dev_up and really use it
> from there.
> dev_down is then for serdev close and also still occupy it.
> closing and releasing would then be done in _remove.

The serdev device is bound you driver regardless of whether you open the
port or not, so just use serdev_device_open() and serdev_device_close()
as necessary at probe() if you need to do some setup and then later at
dev_up() and dev_down(), respectively.

Johan