linux-kernel - RE: [PATCH v3 1/5] fpga: dfl: Allow for ports without specific bar space.

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Date:   Tue, 1 Mar 2022 06:50:57 +0000
From:   "Zhang, Tianfei" <tianfei.zhang@...el.com>
To:     "Wu, Hao" <hao.wu@...el.com>, "trix@...hat.com" <trix@...hat.com>,
        "mdf@...nel.org" <mdf@...nel.org>,
        "Xu, Yilun" <yilun.xu@...el.com>,
        "linux-fpga@...r.kernel.org" <linux-fpga@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "corbet@....net" <corbet@....net>,
        Matthew Gerlach <matthew.gerlach@...ux.intel.com>
Subject: RE: [PATCH v3 1/5] fpga: dfl: Allow for ports without specific bar
 space.



> -----Original Message-----
> From: Wu, Hao <hao.wu@...el.com>
> Sent: Tuesday, March 1, 2022 2:44 PM
> To: Zhang, Tianfei <tianfei.zhang@...el.com>; trix@...hat.com;
> mdf@...nel.org; Xu, Yilun <yilun.xu@...el.com>; linux-fpga@...r.kernel.org;
> linux-doc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org; corbet@....net; Matthew Gerlach
> <matthew.gerlach@...ux.intel.com>
> Subject: RE: [PATCH v3 1/5] fpga: dfl: Allow for ports without specific bar space.
> 
> > -----Original Message-----
> > From: Zhang, Tianfei <tianfei.zhang@...el.com>
> > Sent: Tuesday, March 1, 2022 2:21 PM
> > To: Wu, Hao <hao.wu@...el.com>; trix@...hat.com; mdf@...nel.org; Xu,
> > Yilun <yilun.xu@...el.com>; linux-fpga@...r.kernel.org;
> > linux-doc@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org; corbet@....net; Matthew Gerlach
> > <matthew.gerlach@...ux.intel.com>; Zhang, Tianfei
> > <tianfei.zhang@...el.com>
> > Subject: [PATCH v3 1/5] fpga: dfl: Allow for ports without specific bar space.
> >
> > From: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
> >
> > In OFS, there is a Port device for each PR slot, like Port control,
> > Port user clock control and Port errors, those feature devices are
> > linked with DFL. The DFL of Port device was located in PCIe Bar 0 MMIO
> > space by default, but it also can put into any
> 
> There is not default BAR for Port. In OFS implementation it could be 0, but not
> default value for other implementation.
> 
> > PCIe Bar space. If the BarID (3bits field) in PORTn_OFFSET register
> > set to invalid means that DFL of Port device is located in the Bar 0
> > by default, in this case, it don't need add the Bar 0 into dfl list
> > twice.
> 
> So why not just use existing method (e.g. BAR0 + offset) to locate DFL of port?

For N6000 card, this BarID in PORTn_OFFSET register was set to 0b111 in RTL, which is larger than the maximum PCI BAR numbe PCI_STD_NUM_BARS,
So for software perspective, this means there is no additional the BAR space of this port device, but the DFH of this port device
still located in BAR0.

> 
> The title is confusing too, PORTs still have its BAR location/space.
> 
> Hao
> 
> >
> > ---
> > v2: use FME_HDR_NO_PORT_BAR instead of PCI_STD_NUM_BARS.
> >
> > Signed-off-by: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
> > Signed-off-by: Tianfei Zhang <tianfei.zhang@...el.com>
> > ---
> >  drivers/fpga/dfl-pci.c | 6 ++++++
> >  drivers/fpga/dfl.h     | 1 +
> >  2 files changed, 7 insertions(+)
> >
> > diff --git a/drivers/fpga/dfl-pci.c b/drivers/fpga/dfl-pci.c index
> > 4d68719e608f..33545c999c06 100644
> > --- a/drivers/fpga/dfl-pci.c
> > +++ b/drivers/fpga/dfl-pci.c
> > @@ -258,6 +258,12 @@ static int find_dfls_by_default(struct pci_dev *pcidev,
> >  			 */
> >  			bar = FIELD_GET(FME_PORT_OFST_BAR_ID, v);
> >  			offset = FIELD_GET(FME_PORT_OFST_DFH_OFST, v);
> > +			if (bar >= FME_HDR_NO_PORT_BAR) {
> > +				dev_dbg(&pcidev->dev, "skipping port without
> > specific BAR space %d\n",
> > +					bar);
> > +				continue;
> > +			}
> > +
> >  			start = pci_resource_start(pcidev, bar) + offset;
> >  			len = pci_resource_len(pcidev, bar) - offset;
> >
> > diff --git a/drivers/fpga/dfl.h b/drivers/fpga/dfl.h index
> > 53572c7aced0..1fd493e82dd8 100644
> > --- a/drivers/fpga/dfl.h
> > +++ b/drivers/fpga/dfl.h
> > @@ -91,6 +91,7 @@
> >  #define FME_HDR_PORT_OFST(n)	(0x38 + ((n) * 0x8))
> >  #define FME_HDR_BITSTREAM_ID	0x60
> >  #define FME_HDR_BITSTREAM_MD	0x68
> > +#define FME_HDR_NO_PORT_BAR	7
> >
> >  /* FME Fab Capability Register Bitfield */
> >  #define FME_CAP_FABRIC_VERID	GENMASK_ULL(7, 0)	/* Fabric
> > version ID */
> > --
> > 2.26.2