Re: [PATCH v3] cxl: check decoder count for end device

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

On Mon, 24 Oct 2022 08:43:30 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> CXL spec rev3.0 8.2.4.19.1 added definition for up to 32 decoders. It also
> indicates that for devices, only 10 decoders should be advertised. Add
> check on number of decoders greater than 10 for devices and emit warning.
> 
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
I wonder... Should warning say CXL r3.0 spec violation?

Seems possible this might grow in future versions and so it
might be nice to give a hint that it 'might' be valid in a higher spec version?

I don't care strongly either way though.

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

> ---
> 
> v3:
> - Fix commit header and output message to reflect code change from v2.
> 
> v2:
> - Remove decoder count reassignment from violation (Dan)
> 
>  drivers/cxl/core/hdm.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index d1d2caea5c62..c3b756f93261 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -71,9 +71,19 @@ EXPORT_SYMBOL_NS_GPL(devm_cxl_add_passthrough_decoder, CXL);
>  static void parse_hdm_decoder_caps(struct cxl_hdm *cxlhdm)
>  {
>  	u32 hdm_cap;
> +	struct device *dev = &cxlhdm->port->dev;
>  
>  	hdm_cap = readl(cxlhdm->regs.hdm_decoder + CXL_HDM_DECODER_CAP_OFFSET);
>  	cxlhdm->decoder_count = cxl_hdm_decoder_count(hdm_cap);
> +	/*
> +	 * CXL spec rev3.0 8.2.4.19.1 indicates CXL devices shall not advertise
> +	 * more than 10 decoders. Switches and Host Bridges may advertise up to
> +	 * 32 decoders. Set the decoders to 10 for devices if more than 10 are
> +	 * found.
> +	 */
> +	if (is_cxl_endpoint(cxlhdm->port) && cxlhdm->decoder_count > 10)
> +		dev_warn(dev, "Endpoint decoder count (%d) > 10, spec violation!\n",
> +			 cxlhdm->decoder_count);
>  	cxlhdm->target_count =
>  		FIELD_GET(CXL_HDM_DECODER_TARGET_COUNT_MASK, hdm_cap);
>  	if (FIELD_GET(CXL_HDM_DECODER_INTERLEAVE_11_8, hdm_cap))
> 
>