linux-kernel - Re: [PATCH 10/15] cxl/acpi: Extract the RCH's RCRB base address from CEDT

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Date:   Wed, 31 Aug 2022 12:09:09 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
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>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>
Subject: Re: [PATCH 10/15] cxl/acpi: Extract the RCH's RCRB base address
 from CEDT

On Wed, 31 Aug 2022 10:15:58 +0200
Robert Richter <rrichter@....com> wrote:

> The downstream and upstream port Root Complex Register Blocks (RCRBs)
> are needed to control the ports and CXL devices connected to it. It
> also includes the location of the RCH/RCD downstream and upstream port
> component registers in MEMBAR0. Extract the RCRB from the host's CEDT
> entry.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
Hi Robert,

One trivial comment inline.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

> ---
>  drivers/cxl/acpi.c | 43 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
> 
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index b3146b7ae922..439df9df2741 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -365,11 +365,48 @@ struct pci_host_bridge *cxl_find_next_rch(struct pci_host_bridge *host)
>  	return NULL;
>  }
>  
> +static int __cxl_get_rcrb(union acpi_subtable_headers *header, void *arg,
> +			  const unsigned long end)
> +{
> +	struct cxl_chbs_context *ctx = arg;
> +	struct acpi_cedt_chbs *chbs;
> +
> +	if (ctx->chbcr)
> +		return 0;
> +
> +	chbs = (struct acpi_cedt_chbs *)header;
> +
> +	if (ctx->uid != chbs->uid)
> +		return 0;
> +
> +	if (chbs->cxl_version != ACPI_CEDT_CHBS_VERSION_CXL11)
> +		return 0;
> +
> +	if (chbs->length != SZ_8K)
> +		return 0;
> +
> +	ctx->chbcr = chbs->base;
> +
> +	return 0;
> +}
> +
> +static resource_size_t cxl_get_rcrb(u32 uid)
> +{
> +	struct cxl_chbs_context ctx = {
> +		.uid = uid,
> +	};
> +
> +	acpi_table_parse_cedt(ACPI_CEDT_TYPE_CHBS, __cxl_get_rcrb, &ctx);
> +
> +	return ctx.chbcr;
> +}
> +
>  static int __init cxl_restricted_host_probe(struct platform_device *pdev)
>  {
>  	struct pci_host_bridge *host = NULL;
>  	struct acpi_device *adev;
>  	unsigned long long uid = ~0;
> +	resource_size_t rcrb;

Some of these could be made local to the while loop to reduce their scope.
>  
>  	while ((host = cxl_find_next_rch(host)) != NULL) {
>  		adev = ACPI_COMPANION(&host->dev);
> @@ -382,6 +419,12 @@ static int __init cxl_restricted_host_probe(struct platform_device *pdev)
>  		if (uid > U32_MAX)
>  			continue;
>  
> +		rcrb = cxl_get_rcrb(uid);
> +		if (!rcrb)
> +			continue;
> +
> +		dev_dbg(&host->dev, "RCRB found: 0x%08llx\n", (u64)rcrb);
> +
>  		dev_info(&host->dev, "host supports CXL\n");
>  	}
>