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

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Date:   Mon, 30 Apr 2018 10:26:59 +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:

> On 30/04/2018 06:36, Lee Jones wrote:
> > On Fri, 27 Apr 2018, John Garry wrote:
> > > On 26/04/2018 15:23, John Garry wrote:
> > > > On 26/04/2018 15:08, Mika Westerberg wrote:
> > > > > On Thu, Apr 26, 2018 at 02:49:49PM +0100, John Garry wrote:
> > > > > > diff --git a/drivers/bus/hisi_lpc.c b/drivers/bus/hisi_lpc.c
> > > > > > index 2d4611e..b04425b 100644
> > > > > > --- a/drivers/bus/hisi_lpc.c
> > > > > > +++ b/drivers/bus/hisi_lpc.c
> > > > > > @@ -18,6 +18,8 @@
> > > > > >  #include <linux/of_platform.h>
> > > > > >  #include <linux/pci.h>
> > > > > >  #include <linux/slab.h>
> > > > > > +#include <linux/serial_8250.h>
> > > > > > +#include "../tty/serial/8250/8250.h"
> > > > > > 
> > > > > >  #define DRV_NAME "hisi-lpc"
> > > > > > 
> > > > > > @@ -345,6 +347,7 @@ static void hisi_lpc_comm_outs(void *hostdata,
> > > > > > unsigned
> > > > > > long pio,
> > > > > >  #define MFD_CHILD_NAME_LEN (ACPI_ID_LEN +
> > > > > > sizeof(MFD_CHILD_NAME_PREFIX) -
> > > > > > 1)
> > > > > > 
> > > > > >  struct hisi_lpc_mfd_cell {
> > > > > > +    struct plat_serial8250_port serial8250_port;
> > > > > >      struct mfd_cell_acpi_match acpi_match;
> > > > > >      char name[MFD_CHILD_NAME_LEN];
> > > > > >      char pnpid[ACPI_ID_LEN];
> > > > > > @@ -513,10 +516,31 @@ static int hisi_lpc_acpi_probe(struct device
> > > > > > *hostdev)
> > > > > >          dev_warn(&child->dev, "set resource fail (%d)\n", ret);
> > > > > >              return ret;
> > > > > >          }
> > > > > > +    if (!strcmp(acpi_device_hid(child), "HISI1031")) {
> > > > > 
> > > > 
> > > > Hi Mika,
> > > > 
> > > > > Hmm, there is a way in struct mfd_cell to match child devices using _HID
> > > > > so is there something preventing you from using that?
> > > > 
> > > > Not that I know about. Can you describe this method? I guess I also
> > > > don't need to set the mfd_cell pnpid either for this special case device.
> > > > 
> > > 
> > > 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.

> Anyway, I'll cc you in my next patchset and maybe you can kindly check it.
> 

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