Re: [PATCH v12 1/8] cxl/mbox: Flag support for Dynamic Capacity Devices (DCD)

On Fri, Jul 31, 2026 at 01:48:06AM -0700, Anisa Su wrote:
> From: Ira Weiny <[email protected]>
> 
> Per the CXL 4.0 specification software must check the Command Effects
> Log (CEL) for dynamic capacity command support.
> 
> Detect support for the DCD commands while reading the CEL, including:
> 
>         Get DC Config
>         Get DC Extent List
>         Add DC Response
>         Release DC
> 
> Based on an original patch by Navneet Singh.
> 
> Signed-off-by: Ira Weiny <[email protected]>
> Signed-off-by: Anisa Su <[email protected]>
> Tested-by: Wonjae Lee <[email protected]>
> Tested-by: Junhee Park <[email protected]>
> Tested-by: Heesoo Kim <[email protected]>
> 
> ---
> Changes:
> 1. mbox.c: leave mds->dcd_supported false so the hardware enablement
>    patches can be upstreamed ahead of the extent and DAX work; the
>    event handling patch re-enables it.
> ---
>  drivers/cxl/core/mbox.c | 44 +++++++++++++++++++++++++++++++++++++++++
>  drivers/cxl/cxlmem.h    | 20 +++++++++++++++++++
>  2 files changed, 64 insertions(+)
> 
> diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> index 7c6c5b7450a5..4790524c32a7 100644
> --- a/drivers/cxl/core/mbox.c
> +++ b/drivers/cxl/core/mbox.c
> @@ -165,6 +165,38 @@ static void cxl_set_security_cmd_enabled(struct cxl_security_state *security,
>  	}
>  }
>  
> +static bool cxl_is_dcd_command(u16 opcode)
> +{
> +#define CXL_MBOX_OP_DCD_CMDS 0x48
> +
> +	return (opcode >> 8) == CXL_MBOX_OP_DCD_CMDS;
> +}
> +
> +static void cxl_set_dcd_cmd_enabled(u16 opcode, unsigned long *cmd_mask)
> +{
> +	switch (opcode) {
> +	case CXL_MBOX_OP_GET_DC_CONFIG:
> +		set_bit(CXL_DCD_ENABLED_GET_CONFIG, cmd_mask);
> +		break;
> +	case CXL_MBOX_OP_GET_DC_EXTENT_LIST:
> +		set_bit(CXL_DCD_ENABLED_GET_EXTENT_LIST, cmd_mask);
> +		break;
> +	case CXL_MBOX_OP_ADD_DC_RESPONSE:
> +		set_bit(CXL_DCD_ENABLED_ADD_RESPONSE, cmd_mask);
> +		break;
> +	case CXL_MBOX_OP_RELEASE_DC:
> +		set_bit(CXL_DCD_ENABLED_RELEASE, cmd_mask);
> +		break;
> +	default:
> +		break;
> +	}
> +}
> +
> +static bool cxl_verify_dcd_cmds(unsigned long *cmds_seen)
> +{
> +	return bitmap_full(cmds_seen, CXL_DCD_ENABLED_MAX);
> +}
> +
>  static bool cxl_is_poison_command(u16 opcode)
>  {
>  #define CXL_MBOX_OP_POISON_CMDS 0x43
> @@ -757,6 +789,7 @@ static void cxl_walk_cel(struct cxl_memdev_state *mds, size_t size, u8 *cel)
>  	struct cxl_mailbox *cxl_mbox = &mds->cxlds.cxl_mbox;
>  	struct cxl_cel_entry *cel_entry;
>  	const int cel_entries = size / sizeof(*cel_entry);
> +	DECLARE_BITMAP(dcd_cmds, CXL_DCD_ENABLED_MAX) = {};
>  	struct device *dev = mds->cxlds.dev;
>  	int i, ro_cmds = 0, wr_cmds = 0;
>  
> @@ -785,11 +818,22 @@ static void cxl_walk_cel(struct cxl_memdev_state *mds, size_t size, u8 *cel)
>  			enabled++;
>  		}
>  
> +		if (cxl_is_dcd_command(opcode)) {
> +			cxl_set_dcd_cmd_enabled(opcode, dcd_cmds);
> +			enabled++;
> +		}
> +
>  		dev_dbg(dev, "Opcode 0x%04x %s\n", opcode,
>  			enabled ? "enabled" : "unsupported by driver");
>  	}
>  
>  	set_features_cap(cxl_mbox, ro_cmds, wr_cmds);
> +	/*
> +	 * Disabled until event handling implemented.
> +	 */
> +	if (cxl_verify_dcd_cmds(dcd_cmds))
> +		dev_dbg(dev, "Device supports DCD; capability disabled\n");
> +	mds->dcd_supported = false;
>  }

Hi Anisa,

I read and agree with the other reviewers that this does not need to
mirror the poison and security command handling.

The one-use cxl_verify_dcd_cmds() helper still seems excessive. The
bitmap can be checked directly here:

    if (bitmap_full(dcd_cmds, CXL_DCD_ENABLED_MAX))
            dev_dbg(dev, "Device supports DCD; capability disabled\n");

And then once DCD is ready to be enabled, the assignment can become:

    mds->dcd_supported =
            bitmap_full(dcd_cmds, CXL_DCD_ENABLED_MAX);

-- Alison