linux-kernel - Re: [RFC 6/7] mfd: qcom-smd-rpm: Driver for the Qualcomm RPM over SMD

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Message-ID: <20141020072211.GC25349@x1>
Date:	Mon, 20 Oct 2014 08:22:11 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Bjorn Andersson <bjorn.andersson@...ymobile.com>
Cc:	Kumar Gala <galak@...eaurora.org>,
	Andy Gross <agross@...eaurora.org>,
	Arnd Bergmann <arnd@...db.de>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Samuel Ortiz <sameo@...ux.intel.com>
Subject: Re: [RFC 6/7] mfd: qcom-smd-rpm: Driver for the Qualcomm RPM over SMD

On Fri, 17 Oct 2014, Bjorn Andersson wrote:
> On Wed 08 Oct 01:40 PDT 2014, Lee Jones wrote:

[...]

> > > +static struct qcom_smd_driver qcom_smd_rpm_driver = {
> > > +	.probe = qcom_smd_rpm_probe,
> > > +	.remove = qcom_smd_rpm_remove,
> > > +	.callback = qcom_smd_rpm_callback,
> > > +	.driver  = {
> > > +		.name  = "qcom_smd_rpm",
> > > +		.owner = THIS_MODULE,
> > > +		.of_match_table = qcom_smd_rpm_of_match,
> > > +	},
> > > +};
> > > +
> > > +module_qcom_smd_driver(qcom_smd_rpm_driver);
> > 
> > I don't like this.  What's wrong with the existing platform driver
> > code?
> > 
> 
> I started off with having smd child devices as platform drivers and had some
> accessor functions to find the open handles that triggered the probe() and
> register the callback with those. But this didn't feel very sane, so I did
> implemented a custom driver struct and probe prototype to simplify writing
> drivers.
> 
> May I ask why you dislike this? This is how it's done in so many other places
> in the kernel...

I don't believe that's the case.  All owners of their own
module_*_driver() registration calls are busses (see below), whereas
'qcom_smd' is just a driver.  Things would soon get out of control if
we allowed every driver in the kernel to supply their own driver
registration information variants.

$ git grep "^module_.*_driver(" | \
  cut -d: -f2 | cut -d'(' -f1 | sort | uniq

module_acpi_driver
module_amba_driver
module_comedi_driver
module_comedi_pci_driver
module_comedi_pcmcia_driver
module_comedi_usb_driver
module_gameport_driver
module_hid_driver
module_i2c_driver
module_mcb_driver
module_mipi_dsi_driver
module_pci_driver
module_pcmcia_driver
module_platform_driver
module_serio_driver
module_spi_driver
module_spmi_driver
module_usb_composite_driver
module_usb_driver
module_usb_serial_driver
module_virtio_driver

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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