Hi Alison,
On 2/18/2026 7:44 PM, Alison Schofield wrote:
On Tue, Feb 10, 2026 at 06:44:55AM +0000, Smita Koralahalli wrote:
__cxl_decoder_detach() currently resets decoder programming whenever a
region is detached if cxl_config_state is beyond CXL_CONFIG_ACTIVE. For
Not sure 'detached' is the right word. Unregistered maybe?
autodiscovered regions, this can incorrectly tear down decoder state
that may be relied upon by other consumers or by subsequent ownership
decisions.
Skip cxl_region_decode_reset() during detach when CXL_REGION_F_AUTO is
set.
I get how this is needed in the failover to DAX case, yet I'm not clear
how it fits in with folks that just want to destroy that auto region
and resuse the pieces.
Your other recent patch cxl/hdm: Avoid DVSEC fallback after region teardown[1],
showed me that the memdevs, when left with the endpoint decoders not reset,
will keep trying to create another region when reprobed.
[1] https://lore.kernel.org/linux-cxl/[email protected]/
I think the patch does what it says it does. Perhaps expand on why that
is always the right thing to do.
--Alison
Thanks for the review. I will fix detached to unregistered in the commit
message for v7.
I think there are two paths here: Correct me if I'm wrong.
F_AUTO guard only applies to __cxl_decoder_detach(), which is called
from unregister_region()
(unregister_region()->detach_target()->cxl_decoder_detach()..) path and
via store_targetN()
(store_targetN()->detach_target()->cxl_decoder_detach()..). In both
cases, this patch is preserving decoder state for auto-discovered regions.
When a user explicitly destroys an auto-discovered region via cxl
destroy-region, or decommits via commit_store, those paths call
cxl_region_decode_reset()
(commit_store()->cxl_region_decode_reset()->cxld->reset)
unconditionally, they are not gated by F_AUTO. So users who want to
destroy the auto region and reuse the pieces can still do so. The
decoder state is fully reset in that path.
On the DVSEC fallback fix: The endpoint decoders were being reset (by
cxl_region_decode_reset() unconditionally), which zeroed the registers.
On reprobe, should_emulate_decoders() checked per decoder COMMITTED
bits, found them cleared, and incorrectly fell back to DVSEC range
emulation, treating the decoder as AUTO and creating a spurious region..
Also, since nothing in the dax_hmem path calls unregister_region today,
this F_AUTO guard in __cxl_decoder_detach() is only for preserving
firmware decoder state during auto region teardown. I need to rephrase
that in commit message properly. I will also expand the commit message
for v7 documenting how the explicit decommit path still remains available.
Thanks
Smita
Signed-off-by: Smita Koralahalli <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Reviewed-by: Alejandro Lucero <[email protected]>
---
drivers/cxl/core/region.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index ae899f68551f..45ee598daf95 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -2178,7 +2178,9 @@ __cxl_decoder_detach(struct cxl_region *cxlr,
cxled->part = -1;
if (p->state > CXL_CONFIG_ACTIVE) {
- cxl_region_decode_reset(cxlr, p->interleave_ways);
+ if (!test_bit(CXL_REGION_F_AUTO, &cxlr->flags))
+ cxl_region_decode_reset(cxlr, p->interleave_ways);
+
p->state = CXL_CONFIG_ACTIVE;
}
--
2.17.1
