Re: [PATCH v2 2/2] fpga: dfl: look for vendor specific capability

matthew.gerlach
2020-11-23T17:23:35Z

On Sat, 21 Nov 2020, Moritz Fischer wrote:

> Hi Matthew,
>
> On Wed, Nov 18, 2020 at 11:01:51AM -0800, matthew.gerlach@linux.intel.com wrote:
>> From: Matthew Gerlach <matthew.gerlach@linux.intel.com>
>>
>> A DFL may not begin at offset 0 of BAR 0. A PCIe vendor
>> specific capability can be used to specify the start of a
>> number of DFLs.
>>
>> Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
>> ---
>> v2: Update documentation for clarity.
>> Clean up macro names.
>> Use GENMASK.
>> Removed spurious blank lines.
>> Changed some calls from dev_info to dev_dbg.
>> Specifically check for VSEC not found, -ENODEV.
>> Ensure correct pci vendor id.
>> Remove check for page alignment.
>> Rename find_dfl_in_cfg to find_dfls_by_vsec.
>> Initialize target memory of pci_read_config_dword to invalid values before use.
>> ---
>> Documentation/fpga/dfl.rst | 13 ++++++
>> drivers/fpga/dfl-pci.c | 87 +++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 98 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/fpga/dfl.rst b/Documentation/fpga/dfl.rst
>> index 0404fe6ffc74..37016ff35a90 100644
>> --- a/Documentation/fpga/dfl.rst
>> +++ b/Documentation/fpga/dfl.rst
>> @@ -501,6 +501,19 @@ Developer only needs to provide a sub feature driver with matched feature id.
>> FME Partial Reconfiguration Sub Feature driver (see drivers/fpga/dfl-fme-pr.c)
>> could be a reference.
>>
>> +Location of DFLs on PCI Device
>> +===========================
>
> Maybe start with: "There are two ways of locating the DFLs"

This seems to be a reasonable suggestion. I will update the text.

>> +The start of the first DFL is assumed to be offset 0 of bar 0.
>> +If the first node of the DFL is an FME, then further DFLs
>> +in the port(s) are specified in FME header registers.
>> +Alternatively, a vendor specific capability structure can be used to
>> +specify the location of all the DFLs on the device, providing flexibility
>> +for the type of starting node in the DFL. Intel has reserved the
>> +VSEC ID of 0x43 for this purpose. The vendor specific
>> +data begins with a 4 byte vendor specific register for the number of DFLs followed 4 byte
>> +Offset/BIR vendor specific registers for each DFL. Bits 2:0 of Offset/BIR register
>> +indicates the BAR, and bits 31:3 form the 8 byte aligned offset where bits 2:0 are
>> +zero.
> It's nice to have details, thanks! Nit: This could be a table maybe?

I will look into some sort of table if it looks helpful.

>>
>> Open discussion
>> ===============
>> diff --git a/drivers/fpga/dfl-pci.c b/drivers/fpga/dfl-pci.c
>> index b27fae045536..3a6807e3e10c 100644
>> --- a/drivers/fpga/dfl-pci.c
>> +++ b/drivers/fpga/dfl-pci.c
>> @@ -27,6 +27,14 @@
>> #define DRV_VERSION "0.8"
>> #define DRV_NAME "dfl-pci"
>>
>> +#define PCI_VSEC_ID_INTEL_DFLS 0x43
>> +
>> +#define PCI_VNDR_DFLS_CNT 8
>> +#define PCI_VNDR_DFLS_RES 0x0c
>> +
>> +#define PCI_VNDR_DFLS_RES_BAR_MASK GENMASK(2, 0)
>> +#define PCI_VNDR_DFLS_RES_OFF_MASK GENMASK(31, 3)
>> +
>> struct cci_drvdata {
>> struct dfl_fpga_cdev *cdev; /* container device */
>> };
>> @@ -119,8 +127,80 @@ static int *cci_pci_create_irq_table(struct pci_dev *pcidev, unsigned int nvec)
>> return table;
>> }
>>
>> +static int find_dfls_by_vsec(struct pci_dev *pcidev, struct dfl_fpga_enum_info *info)
>> +{
>> + u32 bar, offset, vndr_hdr, dfl_cnt, dfl_res;
>> + int dfl_res_off, i, voff = 0;
>> + resource_size_t start, len;
>> +
>> + if (pcidev->vendor != PCI_VENDOR_ID_INTEL)
>> + return -ENODEV;
>> +
>> + while ((voff = pci_find_next_ext_capability(pcidev, voff, PCI_EXT_CAP_ID_VNDR))) {
>> + vndr_hdr = 0;
>> + pci_read_config_dword(pcidev, voff + PCI_VNDR_HEADER, &vndr_hdr);
> Are there concerns around those failing?

The intent is that failing pci_read_config would be handled by
initializing the target to an invalid value.

>> +
>> + dev_dbg(&pcidev->dev,
>> + "vendor-specific capability id 0x%x, rev 0x%x len 0x%x\n",
>> + PCI_VNDR_HEADER_ID(vndr_hdr),
>> + PCI_VNDR_HEADER_REV(vndr_hdr),
>> + PCI_VNDR_HEADER_LEN(vndr_hdr));
>> +
>> + if (PCI_VNDR_HEADER_ID(vndr_hdr) == PCI_VSEC_ID_INTEL_DFLS)
>> + break;
>> + }
>> +
>> + if (!voff) {
>> + dev_dbg(&pcidev->dev, "%s no VSEC found\n", __func__);
>> + return -ENODEV;
>> + }
>> +
>> + dfl_cnt = 0;
>> + pci_read_config_dword(pcidev, voff + PCI_VNDR_DFLS_CNT, &dfl_cnt);
> I guess this could fall on it's face if you'd read back ~0 ... maybe
> I'm being too paranoid :)

I don't think you are being too paranoid. I can add a check to make sure
dfl_res_off never outgrows the size of PCIe config space.

>> + dev_dbg(&pcidev->dev, "dfl_cnt %d\n", dfl_cnt);
>> + for (i = 0; i < dfl_cnt; i++) {
>> + dfl_res_off = voff + PCI_VNDR_DFLS_RES +
>> + (i * sizeof(dfl_res));
>> + dfl_res = GENMASK(31, 0);
>> + pci_read_config_dword(pcidev, dfl_res_off, &dfl_res);
>> +
>> + dev_dbg(&pcidev->dev, "dfl_res 0x%x\n", dfl_res);
>> +
>> + bar = dfl_res & PCI_VNDR_DFLS_RES_BAR_MASK;
>> + if (bar >= PCI_STD_NUM_BARS) {
>> + dev_err(&pcidev->dev, "%s bad bar number %d\n",
>> + __func__, bar);
>> + return -EINVAL;
>> + }
>> +
>> + len = pci_resource_len(pcidev, bar);
>> + if (len == 0) {
>> + dev_err(&pcidev->dev, "%s unmapped bar number %d\n",
>> + __func__, bar);
>> + return -EINVAL;
>> + }
>> +
>> + offset = dfl_res & PCI_VNDR_DFLS_RES_OFF_MASK;
>> + if (offset >= len) {
>> + dev_err(&pcidev->dev, "%s bad offset %u >= %pa\n",
>> + __func__, offset, &len);
>> + return -EINVAL;
>> + }
>> +
>> + dev_dbg(&pcidev->dev, "%s BAR %d offset 0x%x\n", __func__, bar, offset);
>> +
>> + len -= offset;
>> +
>> + start = pci_resource_start(pcidev, bar) + offset;
>> +
>> + dfl_fpga_enum_info_add_dfl(info, start, len);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> static int find_dfls_by_default(struct pci_dev *pcidev,
>> - struct dfl_fpga_enum_info *info)
>> + struct dfl_fpga_enum_info *info)
>> {
>> resource_size_t start, len;
>> int port_num, bar, i;
>> @@ -220,7 +300,10 @@ static int cci_enumerate_feature_devs(struct pci_dev *pcidev)
>> goto irq_free_exit;
>> }
>>
>> - ret = find_dfls_by_default(pcidev, info);
>> + ret = find_dfls_by_vsec(pcidev, info);
>> + if (ret == -ENODEV)
>> + ret = find_dfls_by_default(pcidev, info);
>> +
>> if (ret)
>> goto irq_free_exit;
>>
>> --
>> 2.25.2
>>
>
> Thanks,
> Moritz
>