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Subject: Re: [PATCH 2/2] fpga: dfl: look for vendor specific capability
To:     matthew.gerlach@linux.intel.com, linux-fpga@vger.kernel.org,
        linux-kernel@vger.kernel.org, mdf@kernel.org, hao.wu@intel.com,
        linux-doc@vger.kernel.org, corbet@lwn.net
References: <20201117012552.262149-1-matthew.gerlach@linux.intel.com>
 <20201117012552.262149-3-matthew.gerlach@linux.intel.com>
From:   Tom Rix <trix@redhat.com>
Message-ID: <53b9cb12-8002-5737-ba8b-7c59687ead5a@redhat.com>
Date:   Tue, 17 Nov 2020 12:35:19 -0800
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On 11/16/20 5:25 PM, 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>
> ---
>  Documentation/fpga/dfl.rst | 10 +++++
>  drivers/fpga/dfl-pci.c     | 88 +++++++++++++++++++++++++++++++++++++-
>  2 files changed, 97 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/fpga/dfl.rst b/Documentation/fpga/dfl.rst
> index 0404fe6ffc74..c81ceb1e79e2 100644
> --- a/Documentation/fpga/dfl.rst
> +++ b/Documentation/fpga/dfl.rst
> @@ -501,6 +501,16 @@ 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 bus
> +===========================
> +The start of the DFL is assumed to be offset 0 of bar 0.
> +Alternatively, a vendor specific capability structure can be used to
> +specify the location of one or more DFLs.  Intel has reserved the
> +vendor specific id of 0x43 for this purpose.  The vendor specific
> +data begins with a 4 byte count of the number of DFLs followed 4 byte
> +Offset/BIR fields for each DFL. Bits 2:0 of Offset/BIR field indicates
> +the BAR, and bits 31:3 form the 8 byte aligned offset where bits 2:0 are
> +zero.
>  

Does the 'Device Feature List (DFL) Overview' section need to change ?

Maybe some more ascii art on location of bar0 vs vendor specific ?

>  Open discussion
>  ===============
> diff --git a/drivers/fpga/dfl-pci.c b/drivers/fpga/dfl-pci.c
> index b1b157b41942..5418e8bf2496 100644
> --- a/drivers/fpga/dfl-pci.c
> +++ b/drivers/fpga/dfl-pci.c
> @@ -27,6 +27,13 @@
>  #define DRV_VERSION	"0.8"
Since basic pci functionality is changing, consider incrementing this version.
>  #define DRV_NAME	"dfl-pci"
>  
> +#define PCI_VNDR_ID_DFLS 0x43
> +
> +#define PCI_VNDR_DFLS_CNT_OFFSET 8
> +#define PCI_VNDR_DFLS_RES_OFFSET 0x0c
> +
> +#define PCI_VND_DFLS_RES_BAR_MASK 0x7
Is this missing a R? PCI_VNDR_DFLS_RES_BAR_MASK ?
> +
>  struct cci_drvdata {
>  	struct dfl_fpga_cdev *cdev;	/* container device */
>  };
> @@ -119,6 +126,82 @@ static int *cci_pci_create_irq_table(struct pci_dev *pcidev, unsigned int nvec)
>  	return table;
>  }
>  
> +static int find_dfl_in_cfg(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;
> +
> +	while ((voff = pci_find_next_ext_capability(pcidev, voff, PCI_EXT_CAP_ID_VNDR))) {
> +
extra nl
> +		pci_read_config_dword(pcidev, voff + PCI_VNDR_HEADER, &vndr_hdr);

A general problem.

Return of pci_read is not checked, nor are the values ex/ vndr_hdr initialized.

> +
> +		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_VNDR_ID_DFLS)
> +			break;
> +	}
> +
> +	if (!voff) {
> +		dev_dbg(&pcidev->dev, "%s no VSEC found\n", __func__);
> +		return -ENODEV;
> +	}
> +
> +	pci_read_config_dword(pcidev, voff + PCI_VNDR_DFLS_CNT_OFFSET, &dfl_cnt);
> +	dev_info(&pcidev->dev, "dfl_cnt %d\n", dfl_cnt);
> +	for (i = 0; i < dfl_cnt; i++) {
Is there a upper limit on the dfl_cnt ? maybe PCI_STD_NUM_BARS ?
> +		dfl_res_off = voff + PCI_VNDR_DFLS_RES_OFFSET +
> +				      (i * sizeof(dfl_res));
> +		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_VND_DFLS_RES_BAR_MASK;
an extra nl, fix the similar ones as well.
> +
> +		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_VND_DFLS_RES_BAR_MASK;
> +
> +		if (offset >= len) {
> +			dev_err(&pcidev->dev, "%s bad offset %u >= %llu\n",
> +				__func__, offset, len);
> +			return -EINVAL;
> +		}
> +
> +		dev_info(&pcidev->dev, "%s BAR %d offset 0x%x\n", __func__, bar, offset);
> +
> +		start = pci_resource_start(pcidev, bar) + offset;
> +		len -= offset;
> +
> +		if (!PAGE_ALIGNED(start)) {
> +			dev_err(&pcidev->dev, "%s unaliged start 0x%llx\n",
> +				__func__, start);
> +			return -EINVAL;
> +		}
> +
> +		dfl_fpga_enum_info_add_dfl(info, start, len);
> +	}
> +
> +	return 0;
> +}
> +
>  static int find_dfl_in_bar0(struct pci_dev *pcidev,
>  			    struct dfl_fpga_enum_info *info)
>  {
> @@ -221,7 +304,10 @@ static int cci_enumerate_feature_devs(struct pci_dev *pcidev)
>  			goto irq_free_exit;
>  	}
>  
> -	ret = find_dfl_in_bar0(pcidev, info);
> +	ret = find_dfl_in_cfg(pcidev, info);
> +
> +	if (ret)
> +		ret = find_dfl_in_bar0(pcidev, info);

Is this really an either/or ?

Could there be a base functionality on bar0 and a skew functionality on vendor bars?

If vendor is going to completely override, why not use bar0 ?

Tom

>  
>  	if (ret)
>  		goto irq_free_exit;