linux-kernel - Re: [PATCH v1 21/29] cxl/region: Lock decoders that need address translation

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Message-ID: <Z32sFDz-gH1tZgmB@gourry-fedora-PF4VCD3F>
Date: Tue, 7 Jan 2025 17:35:00 -0500
From: Gregory Price <gourry@...rry.net>
To: Robert Richter <rrichter@....com>
Cc: Alison Schofield <alison.schofield@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>,
	Terry Bowman <terry.bowman@....com>
Subject: Re: [PATCH v1 21/29] cxl/region: Lock decoders that need address
 translation

On Tue, Jan 07, 2025 at 03:10:07PM +0100, Robert Richter wrote:
> There is only support to translate from the endpoint to its parent
> port, but not in the opposite direction from the parent to the
> endpoint. Thus, the endpoint address range cannot be determined and
> setup manually. If the parent implements the ->to_hpa() callback and
> needs address translation, forbit reprogramming of the decoders and
                             ^^^^^^
                             forbid?

> lock them.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> ---
>  drivers/cxl/core/region.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 8d7893878362..681c26abc26e 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3353,6 +3353,17 @@ static int cxl_endpoint_initialize(struct cxl_endpoint_decoder *cxled)
>  		if (cxl_port_calc_hpa(parent, cxld, &hpa))
>  			return -ENXIO;
>  
> +		/*
> +		 * There is only support to translate from the endpoint to its
> +		 * parent port, but not in the opposite direction from the
> +		 * parent to the endpoint. Thus, the endpoint address range
> +		 * cannot be determined and setup manually. If the parent
> +		 * implements the ->to_hpa() callback and needs address
> +		 * translation, forbit reprogramming of the decoders and lock
                                ^^^^^^
                                forbid?

> +		 * them.
> +		 */
> +		cxld->flags |= CXL_DECODER_F_LOCK;
> +
>  		/* Iterate from endpoint to root_port refining the position */
>  		pos = cxl_port_calc_pos(iter, &hpa, pos);
>  		if (pos < 0)
> -- 
> 2.39.5
>