Re: [RFC PATCH 1/3] pci, acpi: Match PCI config space accessors against platfrom specific ECAM quirks.

[Christopher Covington]

Hi Tomasz,

Thanks for your work on this.

On 06/02/2016 04:41 AM, Tomasz Nowicki wrote:
> Some platforms may not be fully compliant with generic set of PCI config
> accessors. For these cases we implement the way to overwrite accessors
> set. Algorithm traverses available quirk list, matches against
> <oem_id, oem_rev, domain, bus number> tuple and returns corresponding
> PCI config ops. oem_id and oem_rev come from MCFG table standard header.
> All quirks can be defined using DECLARE_ACPI_MCFG_FIXUP() macro and
> kept self contained. Example:
> 
> /* Custom PCI config ops */
> static struct pci_generic_ecam_ops foo_pci_ops = {
> 	.bus_shift	= 24,
> 	.pci_ops = {
> 		.map_bus = pci_ecam_map_bus,
> 		.read = foo_ecam_config_read,
> 		.write = foo_ecam_config_write,
> 	}
> };
> 
> DECLARE_ACPI_MCFG_FIXUP(&foo_pci_ops, <oem_id_str>, <oem_rev>, <domain_nr>, <bus_nr>);
> 
> Signed-off-by: Tomasz Nowicki <tn@xxxxxxxxxxxx>
> ---
>  drivers/acpi/pci_mcfg.c           | 32 ++++++++++++++++++++++++++++++++
>  include/asm-generic/vmlinux.lds.h |  7 +++++++
>  include/linux/pci-acpi.h          | 19 +++++++++++++++++++
>  3 files changed, 58 insertions(+)
> 
> diff --git a/drivers/acpi/pci_mcfg.c b/drivers/acpi/pci_mcfg.c
> index 1847f74..f3d4570 100644
> --- a/drivers/acpi/pci_mcfg.c
> +++ b/drivers/acpi/pci_mcfg.c
> @@ -22,11 +22,43 @@
>  #include <linux/kernel.h>
>  #include <linux/pci.h>
>  #include <linux/pci-acpi.h>
> +#include <linux/pci-ecam.h>
>  
>  /* Root pointer to the mapped MCFG table */
>  static struct acpi_table_mcfg *mcfg_table;
>  static int mcfg_entries;
>  
> +extern struct pci_cfg_fixup __start_acpi_mcfg_fixups[];
> +extern struct pci_cfg_fixup __end_acpi_mcfg_fixups[];
> +
> +struct pci_ecam_ops *pci_mcfg_get_ops(struct acpi_pci_root *root)
> +{
> +	int bus_num = root->secondary.start;
> +	int domain = root->segment;
> +	struct pci_cfg_fixup *f;
> +
> +	if (!mcfg_table)
> +		return &pci_generic_ecam_ops;
> +
> +	/*
> +	 * Match against platform specific quirks and return corresponding
> +	 * CAM ops.
> +	 *
> +	 * First match against PCI topology <domain:bus> then use OEM ID and
> +	 * OEM revision from MCFG table standard header.
> +	 */
> +	for (f = __start_acpi_mcfg_fixups; f < __end_acpi_mcfg_fixups; f++) {
> +		if ((f->domain == domain || f->domain == PCI_MCFG_DOMAIN_ANY) &&
> +		    (f->bus_num == bus_num || f->bus_num == PCI_MCFG_BUS_ANY) &&
> +		    (!strncmp(f->oem_id, mcfg_table->header.oem_id,
> +			      ACPI_OEM_ID_SIZE)) &&
> +		    (f->oem_revision == mcfg_table->header.oem_revision))

Is this more likely to be updated between quirky and fixed platforms
than oem_table_id? What do folks think about using oem_table_id instead
of, or in addition to, oem_revision?

In case these details are helpful, here was my simple prototype of an
MCFG based approach:

https://codeaurora.org/cgit/quic/server/kernel/commit/?h=cov/4.7-rc1-testing&id=c5d8bc49a198fd8f61f82c7d8f169564d6176b07
https://codeaurora.org/cgit/quic/server/kernel/commit/?h=cov/4.7-rc1-testing&id=50bfe77ccd1639e6ce8c7c4fcca187d50e0bead4

Thanks,
Cov

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