Re: [PATCH v28 5/5] sfc: support pio mapping based on cxl

[Dave Jiang <dave.jiang@intel.com>]

On 6/18/26 11:18 AM, alejandro.lucero-palau@amd.com wrote:
> From: Alejandro Lucero <alucerop@amd.com>
> 
> A PIO buffer is a region of device memory to which the driver can write a
> packet for TX, with the device handling the transmit doorbell without
> requiring a DMA for getting the packet data, which helps reducing latency
> in certain exchanges. With CXL mem protocol this latency can be lowered
> further.
> 
> With a device supporting CXL and successfully initialised, use the cxl
> region to map the memory range and use this mapping for PIO buffers.
> 
> Signed-off-by: Alejandro Lucero <alucerop@amd.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>


> ---
>  drivers/net/ethernet/sfc/ef10.c       | 41 ++++++++++++++++++++++-----
>  drivers/net/ethernet/sfc/efx.h        |  1 -
>  drivers/net/ethernet/sfc/efx_cxl.c    |  1 +
>  drivers/net/ethernet/sfc/net_driver.h |  1 +
>  drivers/net/ethernet/sfc/nic.h        |  3 ++
>  5 files changed, 39 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/ethernet/sfc/ef10.c b/drivers/net/ethernet/sfc/ef10.c
> index 7e04f115bbaa..73bc064929f6 100644
> --- a/drivers/net/ethernet/sfc/ef10.c
> +++ b/drivers/net/ethernet/sfc/ef10.c
> @@ -24,6 +24,7 @@
>  #include <linux/wait.h>
>  #include <linux/workqueue.h>
>  #include <net/udp_tunnel.h>
> +#include "efx_cxl.h"
>  
>  /* Hardware control for EF10 architecture including 'Huntington'. */
>  
> @@ -106,7 +107,7 @@ static int efx_ef10_get_vf_index(struct efx_nic *efx)
>  
>  static int efx_ef10_init_datapath_caps(struct efx_nic *efx)
>  {
> -	MCDI_DECLARE_BUF(outbuf, MC_CMD_GET_CAPABILITIES_V4_OUT_LEN);
> +	MCDI_DECLARE_BUF(outbuf, MC_CMD_GET_CAPABILITIES_V7_OUT_LEN);
>  	struct efx_ef10_nic_data *nic_data = efx->nic_data;
>  	size_t outlen;
>  	int rc;
> @@ -177,6 +178,12 @@ static int efx_ef10_init_datapath_caps(struct efx_nic *efx)
>  			  efx->num_mac_stats);
>  	}
>  
> +	if (outlen < MC_CMD_GET_CAPABILITIES_V7_OUT_LEN)
> +		nic_data->datapath_caps3 = 0;
> +	else
> +		nic_data->datapath_caps3 = MCDI_DWORD(outbuf,
> +						      GET_CAPABILITIES_V7_OUT_FLAGS3);
> +
>  	return 0;
>  }
>  
> @@ -1140,6 +1147,9 @@ static int efx_ef10_dimension_resources(struct efx_nic *efx)
>  	unsigned int channel_vis, pio_write_vi_base, max_vis;
>  	struct efx_ef10_nic_data *nic_data = efx->nic_data;
>  	unsigned int uc_mem_map_size, wc_mem_map_size;
> +#ifdef CONFIG_SFC_CXL
> +	struct efx_probe_data *probe_data;
> +#endif
>  	void __iomem *membase;
>  	int rc;
>  
> @@ -1263,8 +1273,23 @@ static int efx_ef10_dimension_resources(struct efx_nic *efx)
>  	iounmap(efx->membase);
>  	efx->membase = membase;
>  
> -	/* Set up the WC mapping if needed */
> -	if (wc_mem_map_size) {
> +	if (!wc_mem_map_size)
> +		goto skip_pio;
> +
> +	/* Set up the WC mapping */
> +
> +#ifdef CONFIG_SFC_CXL
> +	probe_data = container_of(efx, struct efx_probe_data, efx);
> +	if ((nic_data->datapath_caps3 &
> +	    (1 << MC_CMD_GET_CAPABILITIES_V7_OUT_CXL_CONFIG_ENABLE_LBN)) &&
> +	    probe_data->cxl_pio_initialised) {
> +		/* Using PIO through CXL mapping */
> +		nic_data->pio_write_base = probe_data->cxl->ctpio_cxl;
> +		nic_data->pio_write_vi_base = pio_write_vi_base;
> +	} else
> +#endif
> +	{
> +		/* Using legacy PIO BAR mapping */
>  		nic_data->wc_membase = ioremap_wc(efx->membase_phys +
>  						  uc_mem_map_size,
>  						  wc_mem_map_size);
> @@ -1279,12 +1304,14 @@ static int efx_ef10_dimension_resources(struct efx_nic *efx)
>  			nic_data->wc_membase +
>  			(pio_write_vi_base * efx->vi_stride + ER_DZ_TX_PIOBUF -
>  			 uc_mem_map_size);
> -
> -		rc = efx_ef10_link_piobufs(efx);
> -		if (rc)
> -			efx_ef10_free_piobufs(efx);
>  	}
>  
> +	rc = efx_ef10_link_piobufs(efx);
> +	if (rc)
> +		efx_ef10_free_piobufs(efx);
> +
> +skip_pio:
> +
>  	netif_dbg(efx, probe, efx->net_dev,
>  		  "memory BAR at %pa (virtual %p+%x UC, %p+%x WC)\n",
>  		  &efx->membase_phys, efx->membase, uc_mem_map_size,
> diff --git a/drivers/net/ethernet/sfc/efx.h b/drivers/net/ethernet/sfc/efx.h
> index 45e191686625..057d30090894 100644
> --- a/drivers/net/ethernet/sfc/efx.h
> +++ b/drivers/net/ethernet/sfc/efx.h
> @@ -236,5 +236,4 @@ static inline bool efx_rwsem_assert_write_locked(struct rw_semaphore *sem)
>  
>  int efx_xdp_tx_buffers(struct efx_nic *efx, int n, struct xdp_frame **xdpfs,
>  		       bool flush);
> -
>  #endif /* EFX_EFX_H */
> diff --git a/drivers/net/ethernet/sfc/efx_cxl.c b/drivers/net/ethernet/sfc/efx_cxl.c
> index 3e7c950f83e9..348d7404cd7a 100644
> --- a/drivers/net/ethernet/sfc/efx_cxl.c
> +++ b/drivers/net/ethernet/sfc/efx_cxl.c
> @@ -88,6 +88,7 @@ int efx_cxl_init(struct efx_probe_data *probe_data)
>  		return -ENOMEM;
>  	}
>  
> +	probe_data->cxl_pio_initialised = true;
>  	probe_data->cxl = cxl;
>  
>  	return 0;
> diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
> index de3fc9537662..3964b2c56609 100644
> --- a/drivers/net/ethernet/sfc/net_driver.h
> +++ b/drivers/net/ethernet/sfc/net_driver.h
> @@ -1213,6 +1213,7 @@ struct efx_probe_data {
>  	struct efx_nic efx;
>  #ifdef CONFIG_SFC_CXL
>  	struct efx_cxl *cxl;
> +	bool cxl_pio_initialised;
>  #endif
>  };
>  
> diff --git a/drivers/net/ethernet/sfc/nic.h b/drivers/net/ethernet/sfc/nic.h
> index ec3b2df43b68..7480f9995dfb 100644
> --- a/drivers/net/ethernet/sfc/nic.h
> +++ b/drivers/net/ethernet/sfc/nic.h
> @@ -152,6 +152,8 @@ enum {
>   *	%MC_CMD_GET_CAPABILITIES response)
>   * @datapath_caps2: Further Capabilities of datapath firmware (FLAGS2 field of
>   * %MC_CMD_GET_CAPABILITIES response)
> + * @datapath_caps3: Further Capabilities of datapath firmware (FLAGS3 field of
> + * %MC_CMD_GET_CAPABILITIES response)
>   * @rx_dpcpu_fw_id: Firmware ID of the RxDPCPU
>   * @tx_dpcpu_fw_id: Firmware ID of the TxDPCPU
>   * @must_probe_vswitching: Flag: vswitching has yet to be setup after MC reboot
> @@ -187,6 +189,7 @@ struct efx_ef10_nic_data {
>  	bool must_check_datapath_caps;
>  	u32 datapath_caps;
>  	u32 datapath_caps2;
> +	u32 datapath_caps3;
>  	unsigned int rx_dpcpu_fw_id;
>  	unsigned int tx_dpcpu_fw_id;
>  	bool must_probe_vswitching;