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

[Anisa Su <anisa.su887@gmail.com>]

On Tue, Aug 04, 2026 at 09:55:36AM -0700, Alison Schofield wrote:
> On Fri, Jul 31, 2026 at 01:48:06AM -0700, Anisa Su wrote:
> > From: Ira Weiny <iweiny@kernel.org>
> > 
> > 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 <iweiny@kernel.org>
> > Signed-off-by: Anisa Su <anisa.su@samsung.com>
> > Tested-by: Wonjae Lee <wj28.lee@samsung.com>
> > Tested-by: Junhee Park <jh9934.park@samsung.com>
> > Tested-by: Heesoo Kim <habil.kim@samsung.com>
> > 
> > ---
> > 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

Applied :) Thanks Alison!

- Anisa