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[PATCH v2 4/8] cxl/decoder: Drop pointless locking

Dan Williams posted 8 patches 3 months, 3 weeks ago
There is a newer version of this series
[PATCH v2 4/8] cxl/decoder: Drop pointless locking
Posted by Dan Williams 3 months, 3 weeks ago 
cxl_dpa_rwsem coordinates changes to dpa allocation settings for a given
decoder. cxl_decoder_reset() has no need for a consistent snapshot of the
dpa settings since it is merely clearing out whatever was there previously.

Otherwise, cxl_region_rwsem protects against 'reset' racing 'setup'.

In preparationg for converting to rw_semaphore_acquire semantics, drop this
locking.

Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/cxl/core/hdm.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index 81556d12e9b8..e9cb34e30248 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -914,7 +914,6 @@ static void cxl_decoder_reset(struct cxl_decoder *cxld)
 			"%s: out of order reset, expected decoder%d.%d\n",
 			dev_name(&cxld->dev), port->id, port->commit_end);
 
-	down_read(&cxl_dpa_rwsem);
 	ctrl = readl(hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
 	ctrl &= ~CXL_HDM_DECODER0_CTRL_COMMIT;
 	writel(ctrl, hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
@@ -923,7 +922,6 @@ static void cxl_decoder_reset(struct cxl_decoder *cxld)
 	writel(0, hdm + CXL_HDM_DECODER0_SIZE_LOW_OFFSET(id));
 	writel(0, hdm + CXL_HDM_DECODER0_BASE_HIGH_OFFSET(id));
 	writel(0, hdm + CXL_HDM_DECODER0_BASE_LOW_OFFSET(id));
-	up_read(&cxl_dpa_rwsem);
 
 	cxld->flags &= ~CXL_DECODER_F_ENABLE;
 
-- 
2.49.0
Re: [PATCH v2 4/8] cxl/decoder: Drop pointless locking
Posted by Dave Jiang 3 months, 2 weeks ago 

On 6/18/25 10:04 PM, Dan Williams wrote:
> cxl_dpa_rwsem coordinates changes to dpa allocation settings for a given
> decoder. cxl_decoder_reset() has no need for a consistent snapshot of the
> dpa settings since it is merely clearing out whatever was there previously.
> 
> Otherwise, cxl_region_rwsem protects against 'reset' racing 'setup'.
> 
> In preparationg for converting to rw_semaphore_acquire semantics, drop this
> locking.
> 
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Alison Schofield <alison.schofield@intel.com>
> Cc: Vishal Verma <vishal.l.verma@intel.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> ---
>  drivers/cxl/core/hdm.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 81556d12e9b8..e9cb34e30248 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -914,7 +914,6 @@ static void cxl_decoder_reset(struct cxl_decoder *cxld)
>  			"%s: out of order reset, expected decoder%d.%d\n",
>  			dev_name(&cxld->dev), port->id, port->commit_end);
>  
> -	down_read(&cxl_dpa_rwsem);
>  	ctrl = readl(hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
>  	ctrl &= ~CXL_HDM_DECODER0_CTRL_COMMIT;
>  	writel(ctrl, hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> @@ -923,7 +922,6 @@ static void cxl_decoder_reset(struct cxl_decoder *cxld)
>  	writel(0, hdm + CXL_HDM_DECODER0_SIZE_LOW_OFFSET(id));
>  	writel(0, hdm + CXL_HDM_DECODER0_BASE_HIGH_OFFSET(id));
>  	writel(0, hdm + CXL_HDM_DECODER0_BASE_LOW_OFFSET(id));
> -	up_read(&cxl_dpa_rwsem);
>  
>  	cxld->flags &= ~CXL_DECODER_F_ENABLE;
>
Re: [PATCH v2 4/8] cxl/decoder: Drop pointless locking
Posted by Jonathan Cameron 3 months, 2 weeks ago 
On Wed, 18 Jun 2025 22:04:12 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> cxl_dpa_rwsem coordinates changes to dpa allocation settings for a given
> decoder. cxl_decoder_reset() has no need for a consistent snapshot of the
> dpa settings since it is merely clearing out whatever was there previously.
> 
> Otherwise, cxl_region_rwsem protects against 'reset' racing 'setup'.
> 
> In preparationg for converting to rw_semaphore_acquire semantics, drop this

typo

> locking.
> 
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Alison Schofield <alison.schofield@intel.com>
> Cc: Vishal Verma <vishal.l.verma@intel.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

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

> ---
>  drivers/cxl/core/hdm.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 81556d12e9b8..e9cb34e30248 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -914,7 +914,6 @@ static void cxl_decoder_reset(struct cxl_decoder *cxld)
>  			"%s: out of order reset, expected decoder%d.%d\n",
>  			dev_name(&cxld->dev), port->id, port->commit_end);
>  
> -	down_read(&cxl_dpa_rwsem);
>  	ctrl = readl(hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
>  	ctrl &= ~CXL_HDM_DECODER0_CTRL_COMMIT;
>  	writel(ctrl, hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> @@ -923,7 +922,6 @@ static void cxl_decoder_reset(struct cxl_decoder *cxld)
>  	writel(0, hdm + CXL_HDM_DECODER0_SIZE_LOW_OFFSET(id));
>  	writel(0, hdm + CXL_HDM_DECODER0_BASE_HIGH_OFFSET(id));
>  	writel(0, hdm + CXL_HDM_DECODER0_BASE_LOW_OFFSET(id));
> -	up_read(&cxl_dpa_rwsem);
>  
>  	cxld->flags &= ~CXL_DECODER_F_ENABLE;
>
Re: [PATCH v2 4/8] cxl/decoder: Drop pointless locking
Posted by Alison Schofield 3 months, 2 weeks ago 
On Wed, Jun 18, 2025 at 10:04:12PM -0700, Dan Williams wrote:
> cxl_dpa_rwsem coordinates changes to dpa allocation settings for a given
> decoder. cxl_decoder_reset() has no need for a consistent snapshot of the
> dpa settings since it is merely clearing out whatever was there previously.
> 
> Otherwise, cxl_region_rwsem protects against 'reset' racing 'setup'.
> 
> In preparationg for converting to rw_semaphore_acquire semantics, drop this
> locking.
> 

Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Re: [PATCH v2 4/8] cxl/decoder: Drop pointless locking
Posted by Davidlohr Bueso 3 months, 3 weeks ago 
On Wed, 18 Jun 2025, Dan Williams wrote:

>cxl_dpa_rwsem coordinates changes to dpa allocation settings for a given
>decoder. cxl_decoder_reset() has no need for a consistent snapshot of the
>dpa settings since it is merely clearing out whatever was there previously.
>
>Otherwise, cxl_region_rwsem protects against 'reset' racing 'setup'.
>
>In preparationg for converting to rw_semaphore_acquire semantics, drop this
>locking.
>
>Cc: Davidlohr Bueso <dave@stgolabs.net>
>Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
>Cc: Dave Jiang <dave.jiang@intel.com>
>Cc: Alison Schofield <alison.schofield@intel.com>
>Cc: Vishal Verma <vishal.l.verma@intel.com>
>Cc: Ira Weiny <ira.weiny@intel.com>
>Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>

Patchew 2.1-devel-b67e4c2

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