Re: [PATCH] cxl/hdm: Avoid DVSEC fallback after region teardown

[Dave Jiang]

On 2/12/26 3:38 PM, Smita Koralahalli wrote:
> After destroy-region, cxl_region_decode_reset() clears the HDM decoder
> registers (base/size/commit). If the memdev is subsequently bounced
> (disable/enable), port probe re-evaluates decoder capability via
> should_emulate_decoders().
> 
> The existing logic checks each decoder's COMMITTED bit. Since those bits
> are cleared by region teardown, should_emulate_decoders() incorrectly
> falls back to DVSEC range emulation, even though HDM capability is still
> present.
> 
> DVSEC fallback marks the endpoint decoder as AUTO, which triggers
> cxl_add_to_region() -> construct_region(). That path copies the default
> interleave_granularity (4096) into the region parameters. The resulting
> spurious autodiscovered region consumes the CFMWS HPA space and causes a
> subsequent create-region to fail in hpa_alloc().
> 
> Use the global CXL_HDM_DECODER_ENABLE bit instead of per-decoder COMMITTED
> bits to detect HDM capability. If the HDM decoder block is enabled, zeroed
> registers indicate teardown, not absence of HDM support. This prevents the
> unintended DVSEC fallback and subsequent region creation failure.
> 
> Based on cxl/fixes.
> base-commit: 8441c7d3bd6c5a52ab2ecf77e43a5bf262004f5c

This block should go under the '---'

DJ

> 
> Fixes: 52cc48ad2a76 ("cxl/hdm: Limit emulation to the number of range registers")
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@xxxxxxx>
> ---
>  drivers/cxl/core/hdm.c | 25 +++++++++----------------
>  1 file changed, 9 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index eb5a3a7640c6..a0718cbcc355 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -94,7 +94,6 @@ static bool should_emulate_decoders(struct cxl_endpoint_dvsec_info *info)
>  	struct cxl_hdm *cxlhdm;
>  	void __iomem *hdm;
>  	u32 ctrl;
> -	int i;
>  
>  	if (!info)
>  		return false;
> @@ -113,22 +112,16 @@ static bool should_emulate_decoders(struct cxl_endpoint_dvsec_info *info)
>  		return false;
>  
>  	/*
> -	 * If any decoders are committed already, there should not be any
> -	 * emulated DVSEC decoders.
> +	 * If HDM decoders are globally enabled, do not fall back to DVSEC
> +	 * range emulation. Zeroed decoder registers after region teardown
> +	 * do not imply absence of HDM capability.
> +	 *
> +	 * Falling back to DVSEC here would treat the decoder as AUTO and
> +	 * may incorrectly latch default interleave settings.
>  	 */
> -	for (i = 0; i < cxlhdm->decoder_count; i++) {
> -		ctrl = readl(hdm + CXL_HDM_DECODER0_CTRL_OFFSET(i));
> -		dev_dbg(&info->port->dev,
> -			"decoder%d.%d: committed: %ld base: %#x_%.8x size: %#x_%.8x\n",
> -			info->port->id, i,
> -			FIELD_GET(CXL_HDM_DECODER0_CTRL_COMMITTED, ctrl),
> -			readl(hdm + CXL_HDM_DECODER0_BASE_HIGH_OFFSET(i)),
> -			readl(hdm + CXL_HDM_DECODER0_BASE_LOW_OFFSET(i)),
> -			readl(hdm + CXL_HDM_DECODER0_SIZE_HIGH_OFFSET(i)),
> -			readl(hdm + CXL_HDM_DECODER0_SIZE_LOW_OFFSET(i)));
> -		if (FIELD_GET(CXL_HDM_DECODER0_CTRL_COMMITTED, ctrl))
> -			return false;
> -	}
> +	ctrl = readl(hdm + CXL_HDM_DECODER_CTRL_OFFSET);
> +	if (ctrl & CXL_HDM_DECODER_ENABLE)
> +		return false;
>  
>  	return true;
>  }