linux-kernel - Re: [PATCH V4 17/23] acpi, mcfg: Add default PCI config accessors implementation and initial support for related quirks.

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Message-ID: <CAKc_7PWD_jcj323q9moSd4urc7FD1gr9KLqBL+Ox60Mv+zsrmQ@mail.gmail.com>
Date:	Mon, 29 Feb 2016 13:33:41 +0530
From:	Jayachandran Chandrashekaran Nair 
	<jayachandran.chandrashekaran@...adcom.com>
To:	Tomasz Nowicki <tn@...ihalf.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	okaya@...eaurora.org, jiang.liu@...ux.intel.com,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	robert.richter@...iumnetworks.com, Marcin Wojtas <mw@...ihalf.com>,
	Liviu.Dudau@....com, David Daney <ddaney@...iumnetworks.com>,
	wangyijing@...wei.com, Suravee.Suthikulpanit@....com,
	msalter@...hat.com, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
	Jayachandran Chandrashekaran Nair <jchandra@...adcom.com>,
	Jon Masters <jcm@...hat.com>
Subject: Re: [PATCH V4 17/23] acpi, mcfg: Add default PCI config accessors
 implementation and initial support for related quirks.

On Thu, Feb 4, 2016 at 10:58 PM, Tomasz Nowicki <tn@...ihalf.com> wrote:
> We use generic accessors from access.c by default. However, we already
> know platforms that need special handling while accessing to PCI config
> space. These platforms will need different accessors set matched against
> platform ID, domain, bus touple. Therefore we are going to add (in future)
> DECLARE_ACPI_MCFG_FIXUP which will register platform specific custom
> accessors. For now, we let pci_mcfg_get_ops to take acpi_pci_root structure
> as an arguments and left some space for quirk matching algorithm.
>
> Signed-off-by: Tomasz Nowicki <tn@...ihalf.com>
> Tested-by: Duc Dang <dhdang@....com>
> Tested-by: Dongdong Liu <liudongdong3@...wei.com>
> Tested-by: Hanjun Guo <hanjun.guo@...aro.org>
> Tested-by: Graeme Gregory <graeme.gregory@...aro.org>
> Tested-by: Sinan Kaya <okaya@...eaurora.org>
> ---
>  drivers/acpi/mcfg.c      | 30 ++++++++++++++++++++++++++++++
>  include/linux/pci-acpi.h |  8 ++++++++
>  2 files changed, 38 insertions(+)
>
> diff --git a/drivers/acpi/mcfg.c b/drivers/acpi/mcfg.c
> index dca4c4e..dfc2d14 100644
> --- a/drivers/acpi/mcfg.c
> +++ b/drivers/acpi/mcfg.c
> @@ -34,6 +34,36 @@ int __weak raw_pci_write(unsigned int domain, unsigned int bus,
>         return PCIBIOS_DEVICE_NOT_FOUND;
>  }
>
> +void __iomem *
> +pci_mcfg_dev_base(struct pci_bus *bus, unsigned int devfn, int offset)
> +{
> +       struct pci_mmcfg_region *cfg;
> +
> +       cfg = pci_mmconfig_lookup(pci_domain_nr(bus), bus->number);

In the existing code, calls to pci_mmconfig_lookup() is done inside an
rcu_read_lock/rcu_read_unlock pair. Any reason that is not required here?

Also, you can avoid having to do the lookup every time by saving a cfg pointer
see http://lists.infradead.org/pipermail/linux-arm-kernel/2016-January/396921.html


> +       if (cfg && cfg->virt)
> +               return cfg->virt +
> +                       (PCI_MMCFG_BUS_OFFSET(bus->number) | (devfn << 12)) +
> +                       offset;

PCI_MMCFG_OFFSET(bus->number, devfn) would be better

> +       return NULL;
> +}
> +
> +/* Default generic PCI config accessors */
> +static struct pci_ops default_pci_mcfg_ops = {
> +       .map_bus = pci_mcfg_dev_base,
> +       .read = pci_generic_config_read,
> +       .write = pci_generic_config_write,
> +};
> +
> +struct pci_ops *pci_mcfg_get_ops(struct acpi_pci_root *root)
> +{
> +       /*
> +        * TODO: Match against platform specific quirks and return
> +        * corresponding PCI config space accessor set.
> +        */
> +
> +       return &default_pci_mcfg_ops;
> +}

Is it necessary to make these non-static, even in the next patch, the
functions are only used from this file.

> +
>  int __init acpi_parse_mcfg(struct acpi_table_header *header)
>  {
>         struct acpi_table_mcfg *mcfg;
> diff --git a/include/linux/pci-acpi.h b/include/linux/pci-acpi.h
> index 65b91f3..c974586 100644
> --- a/include/linux/pci-acpi.h
> +++ b/include/linux/pci-acpi.h
> @@ -83,10 +83,18 @@ void acpi_pci_remove_bus(struct pci_bus *bus);
>  #ifdef CONFIG_PCI_MMCONFIG
>  int pci_mmcfg_setup_map(struct acpi_pci_root_info *ci);
>  void pci_mmcfg_teardown_map(struct acpi_pci_root_info *ci);
> +struct pci_ops *pci_mcfg_get_ops(struct acpi_pci_root *root);
> +void __iomem *
> +pci_mcfg_dev_base(struct pci_bus *bus, unsigned int devfn, int offset);
>  #else
>  static inline int pci_mmcfg_setup_map(struct acpi_pci_root_info *ci)
>  { return 0; }
>  static inline void pci_mmcfg_teardown_map(struct acpi_pci_root_info *ci) { }
> +static inline struct pci_ops *pci_mcfg_get_ops(struct acpi_pci_root *root)
> +{ return NULL; }
> +static inline void __iomem *
> +pci_mcfg_dev_base(struct pci_bus *bus, unsigned int devfn, int offset)
> +{ return NULL; }
>  #endif
>  #ifdef CONFIG_ACPI_PCI_SLOT

JC.