Re: [PATCH v5 2/2] ACPI: amba bus probing support

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Mon, Jan 11, 2016 at 05:13:20PM +0200, Andy Shevchenko wrote:
> On Mon, Jan 11, 2016 at 3:26 PM, Aleksey Makarov
> <aleksey.makarov@linaro.org> wrote:
> > From: Graeme Gregory <graeme.gregory@linaro.org>
> >
> > On ARM64 some devices use the AMBA device and not the platform bus for
> > probing so add support for this. Uses a dummy clock for apb_pclk as ACPI
> > does not have a suitable clock representation and to keep the core
> > AMBA bus code unchanged between probing methods.
> >
> 
> My comments below.
> 
> > +++ b/drivers/acpi/acpi_amba.c
> > @@ -0,0 +1,122 @@
> > +
> > +/*
> > + * ACPI support for platform bus type.
> > + *
> > + * Copyright (C) 2015, Linaro Ltd
> > + * Author: Graeme Gregory <graeme.gregory@linaro.org>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + */
> > +
> > +#include <linux/acpi.h>
> > +#include <linux/amba/bus.h>
> > +#include <linux/clkdev.h>
> > +#include <linux/clk-provider.h>
> > +#include <linux/device.h>
> > +#include <linux/err.h>
> > +#include <linux/ioport.h>
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +
> > +#include "internal.h"
> > +
> > +static const struct acpi_device_id amba_id_list[] = {
> > +       {"ARMH0061", 0}, /* PL061 GPIO Device */
> > +       {"", 0},
> > +};
> > +
> > +static void amba_register_dummy_clk(void)
> > +{
> > +       static struct clk *amba_dummy_clk;
> > +
> > +       /* If clock already registered */
> > +       if (amba_dummy_clk)
> > +               return;
> > +
> > +       amba_dummy_clk = clk_register_fixed_rate(NULL, "apb_pclk", NULL,
> > +                                               CLK_IS_ROOT, 0);
> > +       clk_register_clkdev(amba_dummy_clk, "apb_pclk", NULL);
> > +}
> > +
> > +static int amba_handler_attach(struct acpi_device *adev,
> > +                               const struct acpi_device_id *id)
> > +{
> > +       struct amba_device *dev;
> > +       struct resource_entry *rentry;
> > +       struct list_head resource_list;
> > +       bool address_found = false;
> > +       int irq_no = 0;
> > +       int ret;
> > +
> > +       /* If the ACPI node already has a physical device attached, skip it. */
> > +       if (adev->physical_node_count)
> > +               return 0;
> > +
> > +       dev = amba_device_alloc(dev_name(&adev->dev), 0, 0);
> > +       if (!dev) {
> > +               dev_err(&adev->dev, "%s(): amba_device_alloc() failed\n",
> > +                       __func__);
> > +               return -ENOMEM;
> > +       }
> > +
> > +       INIT_LIST_HEAD(&resource_list);
> > +       ret = acpi_dev_get_resources(adev, &resource_list, NULL, NULL);
> > +       if (ret < 0)
> > +               goto err_free;
> > +
> > +       list_for_each_entry(rentry, &resource_list, node) {
> > +               switch (resource_type(rentry->res)) {
> > +               case IORESOURCE_MEM:
> > +                       if (!address_found) {
> > +                               dev->res = *rentry->res;
> 
> dev->res is 0 before this one, right? Could you use this fact instead
> of address_found flag?

amba_device_alloc() zero-initialises everything.  However, dev->res is
a struct resource, and I'd prefer _this_ method that the OT is using
to testing some random part of struct resource.

> > +                               address_found = true;
> > +                       }
> > +                       break;
> > +               case IORESOURCE_IRQ:
> > +                       if (irq_no < AMBA_NR_IRQS)
> > +                               dev->irq[irq_no++] = rentry->res->start;
> > +                       break;
> > +               default:
> > +                       dev_warn(&adev->dev, "Invalid resource\n");
> 
> Why? Isn't possible to have other resources for the devices?

AMBA primecell devices have one memory region, and a number of
interrupts.  Other resource types don't make sense.

> > +                       break;
> > +               }
> > +       }
> > +
> > +       acpi_dev_free_resource_list(&resource_list);
> > +
> > +       /*
> > +        * If the ACPI node has a parent and that parent has a physical device
> > +        * attached to it, that physical device should be the parent of
> > +        * the amba device we are about to create.
> > +        */
> > +       if (adev->parent)
> > +               dev->dev.parent = acpi_get_first_physical_node(adev->parent);
> > +
> > +       ACPI_COMPANION_SET(&dev->dev, adev);
> > +
> > +       ret = amba_device_add(dev, &iomem_resource);
> > +       if (ret) {
> 
> ret < 0?
> 
> What to do if ret > 0? It will be considered as not error. Please,
> check what function returns and adjust this.

Non-zero is treated as an error by amba_device_add().  Doing otherwise
here puts it at odds to the outcome of that function.  This code is fine.

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