Re: [PATCH 05/26] cxl/core: Simplify cxl_dpa_set_mode()

[Davidlohr Bueso]

On Sun, 24 Mar 2024, Ira Weiny wrote:

> cxl_dpa_set_mode() checks the mode for validity two times, once outside
> of the DPA RW semaphore and again within.  The function is not in a
> critical path.  Prior to Dynamic Capacity the extra check was not much
> of an issue.  The addition of DC modes increases the complexity of
> the check.

I agree (also to pick this up regardless of dcd work).

> Simplify the mode check before adding the more complex DC modes.

Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>

> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
>
> ---
> Changes for v1:
> [iweiny: new patch]
> [Jonathan: based on getting rid of the loop in cxl_dpa_set_mode]
> [Jonathan: standardize on resource_size() == 0]
> ---
> drivers/cxl/core/hdm.c | 45 ++++++++++++++++++---------------------------
> 1 file changed, 18 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 7d97790b893d..66b8419fd0c3 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -411,44 +411,35 @@ int cxl_dpa_set_mode(struct cxl_endpoint_decoder *cxled,
> 	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
> 	struct device *dev = &cxled->cxld.dev;
> -	int rc;
>
> +	guard(rwsem_write)(&cxl_dpa_rwsem);
> +	if (cxled->cxld.flags & CXL_DECODER_F_ENABLE)
> +		return -EBUSY;
> +
> +	/*
> +	 * Check that the mode is supported by the current partition
> +	 * configuration
> +	 */
> 	switch (mode) {
> 	case CXL_DECODER_RAM:
> +		if (!resource_size(&cxlds->ram_res)) {
> +			dev_dbg(dev, "no available ram capacity\n");
> +			return -ENXIO;
> +		}
> +		break;
> 	case CXL_DECODER_PMEM:
> +		if (!resource_size(&cxlds->pmem_res)) {
> +			dev_dbg(dev, "no available pmem capacity\n");
> +			return -ENXIO;
> +		}
> 		break;
> 	default:
> 		dev_dbg(dev, "unsupported mode: %d\n", mode);
> 		return -EINVAL;
> 	}
>
> -	down_write(&cxl_dpa_rwsem);
> -	if (cxled->cxld.flags & CXL_DECODER_F_ENABLE) {
> -		rc = -EBUSY;
> -		goto out;
> -	}
> -
> -	/*
> -	 * Only allow modes that are supported by the current partition
> -	 * configuration
> -	 */
> -	if (mode == CXL_DECODER_PMEM && !resource_size(&cxlds->pmem_res)) {
> -		dev_dbg(dev, "no available pmem capacity\n");
> -		rc = -ENXIO;
> -		goto out;
> -	}
> -	if (mode == CXL_DECODER_RAM && !resource_size(&cxlds->ram_res)) {
> -		dev_dbg(dev, "no available ram capacity\n");
> -		rc = -ENXIO;
> -		goto out;
> -	}
> -
> 	cxled->mode = mode;
> -	rc = 0;
> -out:
> -	up_write(&cxl_dpa_rwsem);
> -
> -	return rc;
> +	return 0;
> }
>
> int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
>
> --
> 2.44.0