Re: [PATCH 06/26] cxl/port: Add Dynamic Capacity mode support to endpoint decoders

[Jonathan Cameron]

On Sun, 24 Mar 2024 16:18:09 -0700
ira.weiny@xxxxxxxxx wrote:

> From: Navneet Singh <navneet.singh@xxxxxxxxx>
> 
> Endpoint decoders which are used to map Dynamic Capacity must be
> configured to point to the correct Dynamic Capacity (DC) Region.  The
> decoder mode currently represents the partition the decoder points to
> such as ram or pmem.
> 
> Expand the mode to include DC regions [partitions].
> 
> Signed-off-by: Navneet Singh <navneet.singh@xxxxxxxxx>
> Co-developed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> 
> ---
> Changes for v1:
> [iweiny: eliminate added gotos]
> [iweiny: Mark DC support for 6.10 kernel]
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl | 21 +++++++++++----------
>  drivers/cxl/core/hdm.c                  | 19 +++++++++++++++++++
>  drivers/cxl/core/port.c                 | 16 ++++++++++++++++
>  3 files changed, 46 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index fff2581b8033..8b3efaf6563c 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -316,23 +316,24 @@ Description:
>  
>  
>  What:		/sys/bus/cxl/devices/decoderX.Y/mode
> -Date:		May, 2022
> -KernelVersion:	v6.0
> +Date:		May, 2022, June 2024
> +KernelVersion:	v6.0, v6.10 (dcY)
>  Contact:	linux-cxl@xxxxxxxxxxxxxxx
>  Description:
>  		(RW) When a CXL decoder is of devtype "cxl_decoder_endpoint" it
>  		translates from a host physical address range, to a device local
>  		address range. Device-local address ranges are further split
> -		into a 'ram' (volatile memory) range and 'pmem' (persistent
> -		memory) range. The 'mode' attribute emits one of 'ram', 'pmem',
> -		'mixed', or 'none'. The 'mixed' indication is for error cases
> -		when a decoder straddles the volatile/persistent partition
> -		boundary, and 'none' indicates the decoder is not actively
> -		decoding, or no DPA allocation policy has been set.
> +		into a 'ram' (volatile memory) range, 'pmem' (persistent
> +		memory) range, or Dynamic Capacity (DC) range. The 'mode'
> +		attribute emits one of 'ram', 'pmem', 'dcY', 'mixed', or
> +		'none'. The 'mixed' indication is for error cases when a
> +		decoder straddles the volatile/persistent partition boundary,

I love corners.  What happen if no persistent and decoder straddles
volatile / dc0?  Would only happen if the bios was having fun I think...

> +		and 'none' indicates the decoder is not actively decoding, or
> +		no DPA allocation policy has been set.
>  
>  		'mode' can be written, when the decoder is in the 'disabled'
> -		state, with either 'ram' or 'pmem' to set the boundaries for the
> -		next allocation.
> +		state, with 'ram', 'pmem', or 'dcY' to set the boundaries for
> +		the next allocation.
>  
>  
>  What:		/sys/bus/cxl/devices/decoderX.Y/dpa_resource
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 66b8419fd0c3..e22b6f4f7145 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -255,6 +255,14 @@ static void devm_cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
>  	__cxl_dpa_release(cxled);
>  }
>  
> +static int dc_mode_to_region_index(enum cxl_decoder_mode mode)
> +{
> +	if (mode < CXL_DECODER_DC0 || CXL_DECODER_DC7 < mode)
> +		return -EINVAL;
> +
> +	return mode - CXL_DECODER_DC0;
> +}
> +
>  static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
>  			     resource_size_t base, resource_size_t len,
>  			     resource_size_t skipped)
> @@ -411,6 +419,7 @@ 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)
> @@ -433,6 +442,16 @@ int cxl_dpa_set_mode(struct cxl_endpoint_decoder *cxled,
>  			return -ENXIO;
>  		}
>  		break;
> +	case CXL_DECODER_DC0 ... CXL_DECODER_DC7:
> +		rc = dc_mode_to_region_index(mode);
> +		if (rc < 0)
> +			return rc;

Can't fail, so you could not bother checking..  Seems very unlikely
that function will gain other error cases in the future.

> +
> +		if (resource_size(&cxlds->dc_res[rc]) == 0) {
> +			dev_dbg(dev, "no available dynamic capacity\n");
> +			return -ENXIO;
> +		}
> +		break;
>  	default:
>  		dev_dbg(dev, "unsupported mode: %d\n", mode);
>  		return -EINVAL;
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index e59d9d37aa65..80c0651794eb 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -208,6 +208,22 @@ static ssize_t mode_store(struct device *dev, struct device_attribute *attr,
>  		mode = CXL_DECODER_PMEM;
>  	else if (sysfs_streq(buf, "ram"))
>  		mode = CXL_DECODER_RAM;
> +	else if (sysfs_streq(buf, "dc0"))
> +		mode = CXL_DECODER_DC0;
> +	else if (sysfs_streq(buf, "dc1"))
> +		mode = CXL_DECODER_DC1;
> +	else if (sysfs_streq(buf, "dc2"))
> +		mode = CXL_DECODER_DC2;
> +	else if (sysfs_streq(buf, "dc3"))
> +		mode = CXL_DECODER_DC3;
> +	else if (sysfs_streq(buf, "dc4"))
> +		mode = CXL_DECODER_DC4;
> +	else if (sysfs_streq(buf, "dc5"))
> +		mode = CXL_DECODER_DC5;
> +	else if (sysfs_streq(buf, "dc6"))
> +		mode = CXL_DECODER_DC6;
> +	else if (sysfs_streq(buf, "dc7"))
> +		mode = CXL_DECODER_DC7;

Fully agree with the comment that a string + enum table and search
is probably appropriate here.

>  	else
>  		return -EINVAL;
>  
>