RE: [PATCH 12/14] net: axienet: Autodetect 64-bit DMA capability

[Radhey Shyam Pandey <radheys@xilinx.com>]

> -----Original Message-----
> From: Andre Przywara <andre.przywara@arm.com>
> Sent: Tuesday, January 14, 2020 11:12 PM
> To: Radhey Shyam Pandey <radheys@xilinx.com>
> Cc: David S . Miller <davem@davemloft.net>; Michal Simek
> <michals@xilinx.com>; Robert Hancock <hancock@sedsystems.ca>;
> netdev@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH 12/14] net: axienet: Autodetect 64-bit DMA capability
> 
> On Tue, 14 Jan 2020 17:03:41 +0000
> Radhey Shyam Pandey <radheys@xilinx.com> wrote:
> 
> Hi,
> 
> > > -----Original Message-----
> > > From: Andre Przywara <andre.przywara@arm.com>
> > > Sent: Friday, January 10, 2020 5:24 PM
> > > To: David S . Miller <davem@davemloft.net>; Radhey Shyam Pandey
> > > <radheys@xilinx.com>
> > > Cc: Michal Simek <michals@xilinx.com>; Robert Hancock
> > > <hancock@sedsystems.ca>; netdev@vger.kernel.org; linux-arm-
> > > kernel@lists.infradead.org; linux-kernel@vger.kernel.org
> > > Subject: [PATCH 12/14] net: axienet: Autodetect 64-bit DMA
> > > capability
> > >
> > > When newer revisions of the Axienet IP are configured for a 64-bit
> > > bus,
> > I assume in design axidma address width is set to 64-bits.
> 
> So I wrote "64-bit bus" here, but really meant: "address bus wider than 32 bits".
> In our case it's set to 40 bits, because that's how wide the other busses in the
> system are.
> And we have memory from 2GB to 4GB, and from 34GB till 40GB, but not in-
> between (VExpress/Juno memory layout).
> 
> > If not, please provide an overview of the design connections.
> 
> The exact parameter name from PG021 is: "Address Width (32-64) /
> c_addr_width".
Thanks. It's right.

> 
> > > we *need* to write to the MSB part of the an address registers,
> > > otherwise the IP won't recognise this as a DMA start condition.
> > > This is even true when the actual DMA address comes from the lower 4 GB.
> > >
> > > To autodetect this configuration, at probe time we write all 1's to
> > > such
> > Is reading address width axidma IP user parameter(c_addr_width) from
> > the design not sufficient to detect configured bus width?
> 
> What do you mean by that? Reading from where? Is there a way to access those
> parameters from a running system?
Hardware design data i.e IP parameter can be accessed using hsi in-built commands.
Please refer to ug1138-generating-basic-software-platforms.pdf, chapter-4.
The same flow is used in DT,  xilinx device tree generator parses HDF and read IP 
parameters and populate DT binding.

> 
> Cheers,
> Andre.
> 
> > > an MSB register, and see if any bits stick. If this is configured
> > > for a 32-bit bus, those MSB registers are RES0, so reading back 0
> > > indicates that no MSB writes are necessary.
> > > On the other hands reading anything other than 0 indicated the need
> > > to write the MSB registers, so we set the respective flag.
> > >
> > > For now this leaves the actual DMA mask at 32-bit, as we can't
> > > reliably detect the actually wired number of address lines beyond 32.
> > >
> > > Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> > > ---
> > >  drivers/net/ethernet/xilinx/xilinx_axienet.h  |  1 +
> > > .../net/ethernet/xilinx/xilinx_axienet_main.c | 27
> > > +++++++++++++++++++
> > >  2 files changed, 28 insertions(+)
> > >
> > > diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet.h
> > > b/drivers/net/ethernet/xilinx/xilinx_axienet.h
> > > index 4aea4c23d3bb..4feaaa02819c 100644
> > > --- a/drivers/net/ethernet/xilinx/xilinx_axienet.h
> > > +++ b/drivers/net/ethernet/xilinx/xilinx_axienet.h
> > > @@ -161,6 +161,7 @@
> > >  #define XAE_FCC_OFFSET		0x0000040C /* Flow Control
> > > Configuration */
> > >  #define XAE_EMMC_OFFSET		0x00000410 /* EMAC mode
> > > configuration */
> > >  #define XAE_PHYC_OFFSET		0x00000414 /* RGMII/SGMII
> > > configuration */
> > > +#define XAE_ID_OFFSET		0x000004F8 /* Identification register
> > > */
> > >  #define XAE_MDIO_MC_OFFSET	0x00000500 /* MII Management
> > > Config */
> > >  #define XAE_MDIO_MCR_OFFSET	0x00000504 /* MII Management
> > > Control */
> > >  #define XAE_MDIO_MWD_OFFSET	0x00000508 /* MII Management Write
> > > Data */
> > > diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> > > b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> > > index 133f088d797e..f7f593df0c11 100644
> > > --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> > > +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> > > @@ -151,6 +151,9 @@ static void axienet_dma_out_addr(struct
> > > axienet_local *lp, off_t reg,
> > >  				 dma_addr_t addr)
> > >  {
> > >  	axienet_dma_out32(lp, reg, lower_32_bits(addr));
> > > +
> > > +	if (lp->features & XAE_FEATURE_DMA_64BIT)
> > > +		axienet_dma_out32(lp, reg + 4, upper_32_bits(addr));
> > >  }
> > >
> > >  static void desc_set_phys_addr(struct axienet_local *lp, dma_addr_t
> > > addr, @@ -1934,6 +1937,30 @@ static int axienet_probe(struct
> > > platform_device
> > > *pdev)
> > >  		goto free_netdev;
> > >  	}
> > >
> > > +	/*
> > > +	 * Autodetect the need for 64-bit DMA pointers.
> > > +	 * When the IP is configured for a bus width bigger than 32 bits,
> > > +	 * writing the MSB registers is mandatory, even if they are all 0.
> > > +	 * We can detect this case by writing all 1's to one such register
> > > +	 * and see if that sticks: when the IP is configured for 32 bits
> > > +	 * only, those registers are RES0.
> > > +	 * Those MSB registers were introduced in IP v7.1, which we check first.
> > > +	 */
> > > +	if ((axienet_ior(lp, XAE_ID_OFFSET) >> 24) >= 0x9) {
> > > +		void __iomem *desc = lp->dma_regs +
> > > XAXIDMA_TX_CDESC_OFFSET + 4;
> > > +
> > > +		iowrite32(0x0, desc);
> > > +		if (ioread32(desc) == 0) {	/* sanity check */
> > > +			iowrite32(0xffffffff, desc);
> > > +			if (ioread32(desc) > 0) {
> > > +				lp->features |= XAE_FEATURE_DMA_64BIT;
> > > +				dev_info(&pdev->dev,
> > > +					 "autodetected 64-bit DMA range\n");
> > > +			}
> > > +			iowrite32(0x0, desc);
> > > +		}
> > > +	}
> > > +
> > >  	/* Check for Ethernet core IRQ (optional) */
> > >  	if (lp->eth_irq <= 0)
> > >  		dev_info(&pdev->dev, "Ethernet core IRQ not defined\n");
> > > --
> > > 2.17.1
> >