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Message-ID: <DM5PR12MB1835BCA54E44A71C3D1D808CDA859@DM5PR12MB1835.namprd12.prod.outlook.com>
Date: Thu, 18 Feb 2021 10:20:16 +0000
From: Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Vinod Koul <vkoul@...nel.org>,
Dan Williams <dan.j.williams@...el.com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Krzysztof Wilczyński <kw@...ux.com>,
Lukas Wunner <lukas@...ner.de>
Subject: RE: [PATCH v6 04/15] PCI: Add pci_find_vsec_capability() to find a
specific VSEC
On Wed, Feb 17, 2021 at 22:27:38, Bjorn Helgaas <helgaas@...nel.org>
wrote:
> [+cc Krzysztof, since he commented on a previous version]
> [+cc Lukas, who previously proposed exactly what I suggest below,
> sorry for repeating. I think Lukas was right to propose passing in
> the vendor ID because it makes it easier to read the caller.]
>
> When you post new versions of a series, please cc people who commented
> on previous versions.
Noted.
>
> On Fri, Feb 12, 2021 at 06:37:39PM +0100, Gustavo Pimentel wrote:
> > Adds another helper to ones that already exist called
> > pci_find_vsec_capability. This helper crawls through the device PCI
> > config space searching for a specific ID on the Vendor-Specific Extended
> > Capabilities section.
>
> Add pci_find_vsec_capability() to locate a Vendor-Specific Extended
> Capability with the specified VSEC ID.
> >
> > The Vendor-Specific Extended Capability (VSEC) is a special PCI
> > capability (acts like container) defined by PCI-SIG that allows the one
> > or more proprietary capabilities defined by the vendor which aren't
> > standard or shared between the manufactures.
>
> s/is a special ... by PCI-SIG that//
> s/allows the one/allows one/
> s/the manufactures/manufacturers/ (or maybe "vendors" to match previous use)
Ok, I'll include those changes.
>
> > Signed-off-by: Gustavo Pimentel <gustavo.pimentel@...opsys.com>
> > ---
> > drivers/pci/pci.c | 34 ++++++++++++++++++++++++++++++++++
> > include/linux/pci.h | 2 ++
> > include/uapi/linux/pci_regs.h | 6 ++++++
> > 3 files changed, 42 insertions(+)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index b9fecc2..628aa9f 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -693,6 +693,40 @@ u8 pci_find_ht_capability(struct pci_dev *dev, int ht_cap)
> > EXPORT_SYMBOL_GPL(pci_find_ht_capability);
> >
> > /**
> > + * pci_find_vsec_capability - Find a vendor-specific extended capability
> > + * @dev: PCI device to query
> > + * @cap: vendor-specific capability ID code
> > + *
> > + * Typically this function will be called by the PCI driver, which passes
> > + * through argument the 'struct pci_dev *' already pointing for the device
> > + * config space that is associated with the vendor and device ID which will
> > + * know which ID to search and what to do with it, however, there might be
> > + * cases that this function could be called outside of this scope and
> > + * therefore is the caller responsibility to check the vendor and/or
> > + * device ID first.
>
> This is important because it's a bit subtle. IIUC, each vendor
> (identified by Vendor ID at 0x00 in config space) can define its own
> VSEC IDs, so it can define up to 2^16 == 64K VSEC structures.
>
> Of course there's not room for that many in config space; but the
> point is that the vendor chooses its own VSEC IDs and doesn't need to
> coordinate with anybody.
>
> So a VSEC ID 0x0006 in a Synopsys device (Vendor ID 0x16c3) has
> nothing to do with a VSEC ID 0x0006 in an Intel device (Vendor ID
> 0x8086), and it's up to the caller to make sure it's using the correct
> one.
>
> I wonder if it would help avoid mistakes if we made the interface look
> like this:
>
> u16 pci_find_vsec_capability(struct pci_dev *dev, u16 vendor, int vsec_cap_id)
> {
> if (vendor != dev->vendor)
> return 0;
>
> while ((vsec = ...))
> ...
> }
>
> so calls would look like this:
>
> vsec = pci_find_vsec_capability(dev, PCI_VENDOR_ID_SYNOPSYS, DW_PCIE_VSEC_DMA_ID);
>
> which would make it more obvious that DW_PCIE_VSEC_DMA_ID is only
> valid in a Synopsys device.
>
> The function comment could be something like this:
>
> pci_find_vsec_capability - Find a vendor-specific extended capability
> @dev: PCI device to query
> @vendor: Vendor ID for which capability is defined
> @vsec_cap_id: Vendor-specific capability ID
>
> If @dev has Vendor ID @vendor, search for a VSEC capability with
> VSEC ID @vsec_cap_id. If found, return the capability offset in
> config space; otherwise return 0.
>
> Or maybe it's even more subtle than I thought, and I'm missing
> something :)
Okay, seems reasonable.
>
> > + * Returns the address of the vendor-specific structure that matches the
> > + * requested capability ID code within the device's PCI configuration space
> > + * or 0 if it does not find a match.
> > + */
> > +u16 pci_find_vsec_capability(struct pci_dev *dev, int vsec_cap_id)
> > +{
> > + u16 vsec = 0;
> > + u32 header;
> > +
> > + while ((vsec = pci_find_next_ext_capability(dev, vsec,
> > + PCI_EXT_CAP_ID_VNDR))) {
> > + if (pci_read_config_dword(dev, vsec + PCI_VSEC_HDR,
> > + &header) == PCIBIOS_SUCCESSFUL &&
> > + PCI_VSEC_CAP_ID(header) == vsec_cap_id)
> > + return vsec;
> > + }
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_find_vsec_capability);
> > +
> > +/**
> > * pci_find_parent_resource - return resource region of parent bus of given
> > * region
> > * @dev: PCI device structure contains resources to be searched
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index b32126d..da6ab6a 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -1080,6 +1080,8 @@ struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
> >
> > u64 pci_get_dsn(struct pci_dev *dev);
> >
> > +u16 pci_find_vsec_capability(struct pci_dev *dev, int vsec_cap_id);
>
> Can you put this declaration up with the other "find_capability"
> declarations just a few lines up?
Sure.
>
> > struct pci_dev *pci_get_device(unsigned int vendor, unsigned int device,
> > struct pci_dev *from);
> > struct pci_dev *pci_get_subsys(unsigned int vendor, unsigned int device,
> > diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> > index e709ae8..deae275 100644
> > --- a/include/uapi/linux/pci_regs.h
> > +++ b/include/uapi/linux/pci_regs.h
> > @@ -983,6 +983,12 @@
> > #define PCI_VSEC_HDR 4 /* extended cap - vendor-specific */
> > #define PCI_VSEC_HDR_LEN_SHIFT 20 /* shift for length field */
> >
> > +/* Vendor-Specific Extended Capabilities */
> > +#define PCI_VSEC_HEADER 4 /* Vendor-Specific Header */
> > +#define PCI_VSEC_CAP_ID(x) ((x) & 0xffff)
> > +#define PCI_VSEC_CAP_REV(x) (((x) >> 16) & 0xf)
> > +#define PCI_VSEC_CAP_LEN(x) (((x) >> 20) & 0xfff)
>
> The VSEC #defines are a mess. We have already have some duplication
> and inconsistent names. But I think what you need is already there:
>
> /* Vendor-Specific (VSEC, PCI_EXT_CAP_ID_VNDR) */
> #define PCI_VNDR_HEADER 4 /* Vendor-Specific Header */
> #define PCI_VNDR_HEADER_ID(x) ((x) & 0xffff)
> #define PCI_VNDR_HEADER_REV(x) (((x) >> 16) & 0xf)
> #define PCI_VNDR_HEADER_LEN(x) (((x) >> 20) & 0xfff)
Indeed, I'll use this instead.
>
> > /* SATA capability */
> > #define PCI_SATA_REGS 4 /* SATA REGs specifier */
> > #define PCI_SATA_REGS_MASK 0xF /* location - BAR#/inline */
> > --
> > 2.7.4
> >
-Gustavo
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