netdev - Re: [PATCH v11 18/23] cxl: allow region creation by type2 drivers

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Message-ID: <c5067d20-1804-4c14-b0cc-3e27b119f67a@amd.com>
Date: Tue, 11 Mar 2025 15:06:47 -0500
From: Ben Cheatham <benjamin.cheatham@....com>
To: <alejandro.lucero-palau@....com>
CC: <linux-cxl@...r.kernel.org>, <netdev@...r.kernel.org>,
	<dan.j.williams@...el.com>, <edward.cree@....com>, <davem@...emloft.net>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <edumazet@...gle.com>,
	<dave.jiang@...el.com>, <benjamin.cheatham@....com>
Subject: Re: [PATCH v11 18/23] cxl: allow region creation by type2 drivers

On 3/10/25 4:03 PM, alejandro.lucero-palau@....com wrote:
> From: Alejandro Lucero <alucerop@....com>
> 
> Creating a CXL region requires userspace intervention through the cxl
> sysfs files. Type2 support should allow accelerator drivers to create
> such cxl region from kernel code.
> 
> Adding that functionality and integrating it with current support for
> memory expanders.
> 
> Based on https://lore.kernel.org/linux-cxl/168592159835.1948938.1647215579839222774.stgit@dwillia2-xfh.jf.intel.com/
> 
> Signed-off-by: Alejandro Lucero <alucerop@....com>
> ---
>  drivers/cxl/core/region.c | 133 +++++++++++++++++++++++++++++++++++---
>  drivers/cxl/port.c        |   5 +-
>  include/cxl/cxl.h         |   4 ++
>  3 files changed, 133 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index e24666a419cd..e6fbe00d0623 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -2310,6 +2310,17 @@ static int cxl_region_detach(struct cxl_endpoint_decoder *cxled)
>  	return rc;
>  }
>  
> +int cxl_accel_region_detach(struct cxl_endpoint_decoder *cxled)
> +{
> +	int rc;
> +
> +	guard(rwsem_write)(&cxl_region_rwsem);
> +	cxled->part = -1;
> +	rc = cxl_region_detach(cxled);
> +	return rc;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_accel_region_detach, "CXL");
> +
>  void cxl_decoder_kill_region(struct cxl_endpoint_decoder *cxled)
>  {
>  	down_write(&cxl_region_rwsem);
> @@ -2816,6 +2827,14 @@ cxl_find_region_by_name(struct cxl_root_decoder *cxlrd, const char *name)
>  	return to_cxl_region(region_dev);
>  }
>  
> +static void drop_region(struct cxl_region *cxlr)
> +{
> +	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
> +	struct cxl_port *port = cxlrd_to_port(cxlrd);
> +
> +	devm_release_action(port->uport_dev, unregister_region, cxlr);
> +}
> +

Nit: There are a couple of spots in this file that call the above devm_release_action,
I think it would be good to replace those with a call to this function. You
could also get rid of drop_region() and use devm_release_action() instead.

>  static ssize_t delete_region_store(struct device *dev,
>  				   struct device_attribute *attr,
>  				   const char *buf, size_t len)

[snip]

> +/**
> + * cxl_create_region - Establish a region given an endpoint decoder
> + * @cxlrd: root decoder to allocate HPA
> + * @cxled: endpoint decoder with reserved DPA capacity
> + *
> + * Returns a fully formed region in the commit state and attached to the
> + * cxl_region driver.
> + */
> +struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
> +				     struct cxl_endpoint_decoder *cxled, int ways)

Sorry if I'm behind the times, but is it no longer a requirement for accelerator drivers
to have interleaving disabled (i.e. interleave_ways = 1)?