linux-kernel - Re: [RFC PATCH 1/2] ACPI / PNP: Don't add "enumeration_by

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Date:   Mon, 30 Apr 2018 11:46:47 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     John Garry <john.garry@...wei.com>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        andriy.shevchenko@...ux.intel.com, rjw@...ysocki.net,
        linux-acpi@...r.kernel.org, lenb@...nel.org,
        lorenzo.pieralisi@....com, linux-kernel@...r.kernel.org,
        arnd@...db.de, graeme.gregory@...aro.org, helgaas@...nel.org,
        linuxarm@...wei.com, z.liuxinliang@...ilicon.com,
        "Liguozhu (Kenneth)" <liguozhu@...ilicon.com>
Subject: Re: [RFC PATCH 1/2] ACPI / PNP: Don't add "enumeration_by_parent"
 devices

On Mon, 30 Apr 2018, John Garry wrote:

> > > > > So we using the mfd_cell to match child devices using _HID. At a glance, I
> > > > > don't actually see other drivers to use mfd_cell_acpi_match.pnpid .
> > > > > 
> > > > > Anyway we don't use static tables as we need to update the resources of the
> > > > > cell dynamically. However I do look at a driver like intel_quark_i2c_gpio.c,
> > > > > and this dynamically modifies the value of global mfd_cell array here:
> > > > > https://elixir.bootlin.com/linux/latest/source/drivers/mfd/intel_quark_i2c_gpio.c#L266
> > > > > 
> > > > > I know the cell array is only used at probe time, but this did not look to
> > > > > be good standard practice to me.
> > > > 
> > > > Lots of drivers do this to supply dynamic data.  If there is no other
> > > > sane way of providing such data, it's fine to do.  Although each
> > > > situation should be dealt with on a case-by-case basis.
> > > > 
> > > 
> > > Hi Lee,
> > > 
> > > Thanks for your input.
> > > 
> > > I do see others drivers which use dynamic mem for the mfd_cells (like
> > > cros_ec_dev.c), so what we're doing in this driver already is not totally
> > > unchartered territory. But creating the MFD cells from the ACPI table could
> > > be ...
> > 
> > Right.  I don't normally like mixing platform data technologies (MFD,
> > ACPI and DT).  I normally NACK patches which take information from
> > Device Tree and populate MFD cells with it.  ACPI would be the same I
> > guess.
> 
> Oh, well that is what we have in this driver. So what's the preferred
> approach? Just not use MFD model at all if ACPI/DT needs to be scanned for
> data to create the cells?

I've just seen the driver - yuk!

Why are you using the MFD API outside of MFD anyway?

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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