Re: [RFC 02/13] cxl: introduce cxl_get_hdm_info()

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

On Fri, 20 Sep 2024 15:34:35 -0700
Zhi Wang <zhiw@nvidia.com> wrote:

> CXL core has the information of what CXL register groups a device has.
> When initializing the device, the CXL core probes the register groups
> and saves the information. The probing sequence is quite complicated.
> 
> vfio-cxl requires the HDM register information to emualte the HDM decoder
Hi Zhi,

I know these were a bit rushed out so I'll only comment once.
Give your patch descriptions a spell check (I always forget :)
emulate

> registers.
> 
> Introduce cxl_get_hdm_info() for vfio-cxl to leverage the HDM
> register information in the CXL core. Thus, it doesn't need to implement
> its own probing sequence.
> 
> Signed-off-by: Zhi Wang <zhiw@nvidia.com>
> ---
>  drivers/cxl/core/pci.c        | 28 ++++++++++++++++++++++++++++
>  drivers/cxl/cxlpci.h          |  3 +++
>  include/linux/cxl_accel_mem.h |  2 ++
>  3 files changed, 33 insertions(+)
> 
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index a663e7566c48..7b6c2b6211b3 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -502,6 +502,34 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_hdm_decode_init, CXL);
>  
> +int cxl_get_hdm_info(struct cxl_dev_state *cxlds, u32 *hdm_count,
> +		     u64 *hdm_reg_offset, u64 *hdm_reg_size)
> +{
> +	struct pci_dev *pdev = to_pci_dev(cxlds->dev);
> +	int d = cxlds->cxl_dvsec;
> +	u16 cap;
> +	int rc;
> +
> +	if (!cxlds->reg_map.component_map.hdm_decoder.valid) {
> +		*hdm_reg_offset = *hdm_reg_size = 0;
Probably want to zero out the hdm_count as well?

> +	} else {
> +		struct cxl_component_reg_map *map =
> +			&cxlds->reg_map.component_map;
> +
> +		*hdm_reg_offset = map->hdm_decoder.offset;
> +		*hdm_reg_size = map->hdm_decoder.size;
> +	}
> +
> +	rc = pci_read_config_word(pdev,
> +				  d + CXL_DVSEC_CAP_OFFSET, &cap);
> +	if (rc)
> +		return rc;
> +
> +	*hdm_count = FIELD_GET(CXL_DVSEC_HDM_COUNT_MASK, cap);
> +	return 0;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_get_hdm_info, CXL);