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

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Date:   Tue, 14 Jan 2020 17:03:41 +0000
From:   Radhey Shyam Pandey <radheys@...inx.com>
To:     Andre Przywara <andre.przywara@....com>,
        "David S . Miller" <davem@...emloft.net>
CC:     Michal Simek <michals@...inx.com>,
        Robert Hancock <hancock@...systems.ca>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 12/14] net: axienet: Autodetect 64-bit DMA capability

> -----Original Message-----
> From: Andre Przywara <andre.przywara@....com>
> Sent: Friday, January 10, 2020 5:24 PM
> To: David S . Miller <davem@...emloft.net>; Radhey Shyam Pandey
> <radheys@...inx.com>
> Cc: Michal Simek <michals@...inx.com>; Robert Hancock
> <hancock@...systems.ca>; netdev@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org; linux-kernel@...r.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. 
If not, please provide an overview of the design connections.

> 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?

> 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@....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