linux-kernel - Re: [PATCH v1 1/7] cxl/core: Use guard() to replace open-coded down

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Message-ID: <20250211172631.00001a34@huawei.com>
Date: Tue, 11 Feb 2025 17:26:31 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Li Ming <ming.li@...omail.com>
CC: <dave@...olabs.net>, <dave.jiang@...el.com>, <alison.schofield@...el.com>,
	<vishal.l.verma@...el.com>, <ira.weiny@...el.com>,
	<dan.j.williams@...el.com>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/7] cxl/core: Use guard() to replace open-coded
 down_read/write()

On Tue, 11 Feb 2025 15:57:21 +0800
Li Ming <ming.li@...omail.com> wrote:

> Some down/up_read() and down/up_write() cases can be replaced by a
> guard() simply to drop explicit unlock invoked. It helps to align coding
> style with current CXL subsystem's.
> 
> Signed-off-by: Li Ming <ming.li@...omail.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

I wondered if it was worth doing some early returns and dropping
local variables, but on balance think it isn't worth doing.


> @@ -364,10 +362,9 @@ resource_size_t cxl_dpa_size(struct cxl_endpoint_decoder *cxled)
>  {
>  	resource_size_t size = 0;
>  
> -	down_read(&cxl_dpa_rwsem);
> +	guard(rwsem_read)(&cxl_dpa_rwsem);
>  	if (cxled->dpa_res)
>  		size = resource_size(cxled->dpa_res);

Could return resource_size() here and return 0 below.
I'm not sure it gains us much though. 

> -	up_read(&cxl_dpa_rwsem);
>  
>  	return size;
>  }
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index e8d11a988fd9..e3bb33109ced 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3216,10 +3216,9 @@ static int match_region_by_range(struct device *dev, const void *data)
>  	cxlr = to_cxl_region(dev);
>  	p = &cxlr->params;
>  
> -	down_read(&cxl_region_rwsem);
> +	guard(rwsem_read)(&cxl_region_rwsem);
>  	if (p->res && p->res->start == r->start && p->res->end == r->end)
>  		rc = 1;

could do return 1 here and return 0 but it doesn't gain us much.

> -	up_read(&cxl_region_rwsem);
>  
>  	return rc;
>  }