Re: [PATCH v2 1/6] cxl/mem: Drop DVSEC vs EFI Memory Map sanity check

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Mon, 14 Mar 2022 18:22:22 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> When the driver finds legacy DVSEC ranges active on a CXL Memory
> Expander it indicates that platform firmware is not aware of, or is
> deliberately disabling common CXL 2.0 operation. In this case Linux
> generally has no choice, but to leave the device alone.
> 
> The driver attempts to validate that the DVSEC range is in the EFI
> memory map. Remove that logic since there is no requirement that the
> BIOS publish DVSEC ranges in the EFI Memory Map.
> 
> In the future the driver will want to permanently reserve this capacity
> out of the available CFMWS capacity and hide it from
> request_free_mem_region(), but it serves no purpose to warn about the
> range not appearing in the EFI Memory Map.
> 
> Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
>  drivers/cxl/mem.c |   24 +-----------------------
>  1 file changed, 1 insertion(+), 23 deletions(-)
> 
> diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> index 49a4b1c47299..cd4e8bba82aa 100644
> --- a/drivers/cxl/mem.c
> +++ b/drivers/cxl/mem.c
> @@ -158,30 +158,8 @@ static int cxl_mem_probe(struct device *dev)
>  	 * is no use in trying to manage those.
>  	 */
>  	if (!cxl_dvsec_decode_init(cxlds)) {
> -		struct cxl_endpoint_dvsec_info *info = &cxlds->info;
> -		int i;
> -
> -		/* */
> -		for (i = 0; i < 2; i++) {
> -			u64 base, size;
> -
> -			/*
> -			 * Give a nice warning to the user that BIOS has really
> -			 * botched things for them if it didn't place DVSEC
> -			 * ranges in the memory map.
> -			 */
> -			base = info->dvsec_range[i].start;
> -			size = range_len(&info->dvsec_range[i]);
> -			if (size && !region_intersects(base, size,
> -						       IORESOURCE_SYSTEM_RAM,
> -						       IORES_DESC_NONE)) {
> -				dev_err(dev,
> -					"DVSEC range %#llx-%#llx must be reserved by BIOS, but isn't\n",
> -					base, base + size - 1);
> -			}
> -		}
>  		dev_err(dev,
> -			"Active DVSEC range registers in use. Will not bind.\n");
> +			"Legacy range registers configuration prevents HDM operation.\n");
>  		return -EBUSY;
>  	}
>  
>