Re: [PATCH V8 7/9] acpi: Add generic MCFG table handling

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Mon, May 30, 2016 at 05:14:20PM +0200, Tomasz Nowicki wrote:
> In order to handle PCI config space regions properly in ACPI, new MCFG
> interface is defined which does sanity checks on MCFG table and keeps its
> root pointer. The user is able to lookup MCFG regions based on
> host bridge root structure and domain:bus_start:bus_end touple.
> Use pci_mmcfg_late_init old prototype to avoid another function name.

"According to PCI firmware specifications, on systems booting with ACPI,
PCI configuration for a host bridge must be set-up through the MCFG table
regions for non-hotpluggable bridges and _CBA method for hotpluggable ones.

Current MCFG table handling code, as implemented for x86, cannot be
easily generalized owing to x86 specific quirks handling and related
code, which makes it hard to reuse on other architectures.

In order to implement MCFG PCI configuration handling for new platforms
booting with ACPI (eg ARM64) this patch re-implements MCFG handling from
scratch in a streamlined fashion and provides (through a generic
interface available to all arches):

- Simplified MCFG table parsing (executed through the pci_mmcfg_late_init()
  hook as in current x86)
- MCFG regions look-up interface through domain:bus_start:bus_end tuple

The new MCFG regions handling interface is added to generic ACPI code
so that existing architectures (eg x86) can be moved over to it and
architectures relying on MCFG for ACPI PCI config space can rely on it
without having to resort to arch specific implementations."

> Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
> Signed-off-by: Jayachandran C <jchandra@broadcom.com>
> ---
>  drivers/acpi/Kconfig     |  3 ++
>  drivers/acpi/Makefile    |  1 +
>  drivers/acpi/pci_mcfg.c  | 94 ++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pci-acpi.h |  2 ++
>  include/linux/pci.h      |  2 +-
>  5 files changed, 101 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/acpi/pci_mcfg.c
> 
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index b7e2e77..f98c328 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -217,6 +217,9 @@ config ACPI_PROCESSOR_IDLE
>  	bool
>  	select CPU_IDLE
>  
> +config ACPI_MCFG
> +	bool
> +
>  config ACPI_CPPC_LIB
>  	bool
>  	depends on ACPI_PROCESSOR
> diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
> index 251ce85..632e81f 100644
> --- a/drivers/acpi/Makefile
> +++ b/drivers/acpi/Makefile
> @@ -40,6 +40,7 @@ acpi-$(CONFIG_ARCH_MIGHT_HAVE_ACPI_PDC) += processor_pdc.o
>  acpi-y				+= ec.o
>  acpi-$(CONFIG_ACPI_DOCK)	+= dock.o
>  acpi-y				+= pci_root.o pci_link.o pci_irq.o
> +obj-$(CONFIG_ACPI_MCFG)		+= pci_mcfg.o
>  acpi-y				+= acpi_lpss.o acpi_apd.o
>  acpi-y				+= acpi_platform.o
>  acpi-y				+= acpi_pnp.o
> diff --git a/drivers/acpi/pci_mcfg.c b/drivers/acpi/pci_mcfg.c
> new file mode 100644
> index 0000000..1847f74
> --- /dev/null
> +++ b/drivers/acpi/pci_mcfg.c
> @@ -0,0 +1,94 @@
> +/*
> + * Copyright (C) 2016 Broadcom
> + *	Author: Jayachandran C <jchandra@broadcom.com>
> + * Copyright (C) 2016 Semihalf
> + * 	Author: Tomasz Nowicki <tn@semihalf.com>
> + *
> + * 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 (the "GPL").
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License version 2 (GPLv2) for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * version 2 (GPLv2) along with this source code.
> + */
> +
> +#define pr_fmt(fmt) "ACPI: " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/pci.h>
> +#include <linux/pci-acpi.h>
> +
> +/* Root pointer to the mapped MCFG table */
> +static struct acpi_table_mcfg *mcfg_table;
> +static int mcfg_entries;
> +
> +int pci_mcfg_lookup(struct acpi_pci_root *root)
> +{
> +	struct acpi_mcfg_allocation *mptr, *entry = NULL;
> +	struct resource *bus_res = &root->secondary;
> +	int i;
> +
> +	if (mcfg_table) {
> +		mptr = (struct acpi_mcfg_allocation *) &mcfg_table[1];
> +		for (i = 0; i < mcfg_entries && !entry; i++, mptr++)
> +			if (mptr->pci_segment == root->segment &&
> +			    mptr->start_bus_number == bus_res->start)
> +				entry = mptr;
> +	}
> +
> +	/* not found, use _CBA if available, else error */
> +	if (!entry) {
> +		if (root->mcfg_addr)
> +			return root->mcfg_addr;
> +		pr_err("%04x:%pR MCFG lookup failed\n", root->segment, bus_res);
> +		return -ENOENT;
> +	} else if (root->mcfg_addr && entry->address != root->mcfg_addr) {
> +		pr_warn("%04x:%pR CBA %pa != MCFG %lx, using CBA\n",
> +			root->segment, bus_res, &root->mcfg_addr,
> +			(unsigned long)entry->address);
> +		return 0;
> +	}
> +
> +	/* found matching entry, bus range check */
> +	if (entry->end_bus_number != bus_res->end) {
> +		resource_size_t bus_end = min_t(resource_size_t,
> +					entry->end_bus_number, bus_res->end);
> +		pr_warn("%04x:%pR bus end mismatch, using %02lx\n",
> +			root->segment, bus_res, (unsigned long)bus_end);
> +		bus_res->end = bus_end;
> +	}
> +
> +	if (!root->mcfg_addr)
> +		root->mcfg_addr = entry->address;

Let's hope that no one will ever implement a hotplug bridge with config
space starting at physical address 0x0.

Nit: You should define what the return value means. For success, once you
return the _CBA address, once 0; this should be consistent.

Anyway, this function is not easy to read but it may well be fine, I will let
Bjorn decide what to do with corner cases:

a) _CBA is != 0 and you get a MCFG entry that matches its address (I am
    not sure that capping the _CRS bus numbers is PCI compliant in that case)
b) bus_end capping, either you leave code as-is (that caps also _CRS) or
   just warn and fail if the bus->end numbers mismatch

Pending Bjorn's opinion on the above (and commit log update):

Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

> +	return 0;
> +}
> +
> +static __init int pci_mcfg_parse(struct acpi_table_header *header)
> +{
> +	if (header->length < sizeof(struct acpi_table_mcfg))
> +		return -EINVAL;
> +
> +	mcfg_entries = (header->length - sizeof(struct acpi_table_mcfg)) /
> +					sizeof(struct acpi_mcfg_allocation);
> +	if (mcfg_entries == 0) {
> +		pr_err("MCFG has no entries\n");
> +		return -EINVAL;
> +	}
> +
> +	mcfg_table = (struct acpi_table_mcfg *)header;
> +	pr_info("MCFG table detected, %d entries\n", mcfg_entries);
> +	return 0;
> +}
> +
> +/* Interface called by ACPI - parse and save MCFG table */
> +void __init pci_mmcfg_late_init(void)
> +{
> +	int err = acpi_table_parse(ACPI_SIG_MCFG, pci_mcfg_parse);
> +	if (err)
> +		pr_err("Failed to parse MCFG (%d)\n", err);
> +}
> diff --git a/include/linux/pci-acpi.h b/include/linux/pci-acpi.h
> index 89ab057..e0e6dfc 100644
> --- a/include/linux/pci-acpi.h
> +++ b/include/linux/pci-acpi.h
> @@ -24,6 +24,8 @@ static inline acpi_status pci_acpi_remove_pm_notifier(struct acpi_device *dev)
>  }
>  extern phys_addr_t acpi_pci_root_get_mcfg_addr(acpi_handle handle);
>  
> +extern int pci_mcfg_lookup(struct acpi_pci_root *root);
> +
>  static inline acpi_handle acpi_find_root_bridge_handle(struct pci_dev *pdev)
>  {
>  	struct pci_bus *pbus = pdev->bus;
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index bba4053..9661c85 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1724,7 +1724,7 @@ void pcibios_free_irq(struct pci_dev *dev);
>  extern struct dev_pm_ops pcibios_pm_ops;
>  #endif
>  
> -#ifdef CONFIG_PCI_MMCONFIG
> +#if defined(CONFIG_PCI_MMCONFIG) || defined(CONFIG_ACPI_MCFG)
>  void __init pci_mmcfg_early_init(void);
>  void __init pci_mmcfg_late_init(void);
>  #else
> -- 
> 1.9.1
>