Subject: Re: [PATCH v20 22/22] sfc: support pio mapping based on cxl

From: Jonathan Cameron <[email-masked]>
Date: Wed, 12 Nov 2025 16:24:37 +0000

On Mon, 10 Nov 2025 15:36:57 +0000
[email-masked] wrote:

> From: Alejandro Lucero <[email-masked]>
> 
> 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.
> 
> Add the disabling of those CXL-based PIO buffers if the callback for
> potential cxl endpoint removal by the CXL code happens.
> 
> Signed-off-by: Alejandro Lucero <[email-masked]>
One comment on something I thought you meant you were changing for v20
but haven't.  Not important, so either way:
Reviewed-by: Jonathan Cameron <[email-masked]>

> diff --git a/drivers/net/ethernet/sfc/efx_cxl.c b/drivers/net/ethernet/sfc/efx_cxl.c
> index 79fe99d83f9f..a84ce45398c1 100644
> --- a/drivers/net/ethernet/sfc/efx_cxl.c
> +++ b/drivers/net/ethernet/sfc/efx_cxl.c
> @@ -11,6 +11,7 @@
>  #include <cxl/pci.h>
>  #include "net_driver.h"
>  #include "efx_cxl.h"
> +#include "efx.h"
>  
>  #define EFX_CTPIO_BUFFER_SIZE	SZ_256M
>  
> @@ -20,6 +21,7 @@ int efx_cxl_init(struct efx_probe_data *probe_data)
>  	struct pci_dev *pci_dev = efx->pci_dev;
>  	resource_size_t max_size;
>  	struct efx_cxl *cxl;
> +	struct range range;
>  	u16 dvsec;
>  	int rc;
>  
> @@ -119,19 +121,40 @@ int efx_cxl_init(struct efx_probe_data *probe_data)
>  	cxl->efx_region = cxl_create_region(cxl->cxlrd, &cxl->cxled, 1);
>  	if (IS_ERR(cxl->efx_region)) {
>  		pci_err(pci_dev, "CXL accel create region failed");
> -		cxl_put_root_decoder(cxl->cxlrd);
> -		cxl_dpa_free(cxl->cxled);
> -		return PTR_ERR(cxl->efx_region);
> +		rc = PTR_ERR(cxl->efx_region);
> +		goto err_dpa;

I thought you agreed with moving this err_dpa path into the earlier patch to
reduce churn.  Maybe you already had v20 ready when you replied to the late
v19 feedback on this.  I don't mind much either way as its just a really
minor patch churn thing.

> +	}
> +
> +	rc = cxl_get_region_range(cxl->efx_region, &range);
> +	if (rc) {
> +		pci_err(pci_dev, "CXL getting regions params failed");
> +		goto err_detach;
> +	}
> +
> +	cxl->ctpio_cxl = ioremap(range.start, range.end - range.start + 1);
> +	if (!cxl->ctpio_cxl) {
> +		pci_err(pci_dev, "CXL ioremap region (%pra) failed", &range);
> +		rc = -ENOMEM;
> +		goto err_detach;
>  	}
>  
>  	probe_data->cxl = cxl;
> +	probe_data->cxl_pio_initialised = true;
>  
>  	return 0;
> +
> +err_detach:
> +	cxl_decoder_detach(NULL, cxl->cxled, 0, DETACH_INVALIDATE);
> +err_dpa:
> +	cxl_put_root_decoder(cxl->cxlrd);
> +	cxl_dpa_free(cxl->cxled);
> +	return rc;
>  }