linux-kernel - Re: [PATCH v9 01/19] cxl/mbox: Flag support for Dynamic Capacity Devices (DCD)

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Message-ID: <20250414151950.00001823@huawei.com>
Date: Mon, 14 Apr 2025 15:19:50 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Ira Weiny <ira.weiny@...el.com>
CC: Dave Jiang <dave.jiang@...el.com>, Fan Ni <fan.ni@...sung.com>, "Dan
 Williams" <dan.j.williams@...el.com>, Davidlohr Bueso <dave@...olabs.net>,
	Alison Schofield <alison.schofield@...el.com>, Vishal Verma
	<vishal.l.verma@...el.com>, <linux-cxl@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 01/19] cxl/mbox: Flag support for Dynamic Capacity
 Devices (DCD)

On Sun, 13 Apr 2025 17:52:09 -0500
Ira Weiny <ira.weiny@...el.com> wrote:

> Per the CXL 3.1 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 <ira.weiny@...el.com>


> +
> +static bool cxl_verify_dcd_cmds(struct cxl_memdev_state *mds, unsigned long *cmds_seen)

It's not immediately obvious to me what the right behavior
from something called cxl_verify_dcd_cmds() is.  A comment might help with that.

I think all it does right now is check if any bits are set. In my head
it was going to check that all bits needed for a useful implementation were
set. I did have to go check what a 'logical and' of a bitmap was defined as
because that bit of the bitmap_and() return value wasn't obvious to me either!


> +{
> +	DECLARE_BITMAP(all_cmds, CXL_DCD_ENABLED_MAX);
> +	DECLARE_BITMAP(dst, CXL_DCD_ENABLED_MAX);
> +
> +	bitmap_fill(all_cmds, CXL_DCD_ENABLED_MAX);
> +	return bitmap_and(dst, cmds_seen, all_cmds, CXL_DCD_ENABLED_MAX);
> +}
> +