linux-kernel - Re: [PATCH v3 9/9] cxl/acpi: Set ACPI's CXL

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Message-ID: <20221109233558.GA581582@bhelgaas>
Date:   Wed, 9 Nov 2022 17:35:58 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
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>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, linux-cxl@...r.kernel.org,
        linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Dave Jiang <dave.jiang@...el.com>,
        Terry Bowman <terry.bowman@....com>, linux-pci@...r.kernel.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH v3 9/9] cxl/acpi: Set ACPI's CXL _OSC to indicate CXL1.1
 support

On Wed, Nov 09, 2022 at 11:40:59AM +0100, Robert Richter wrote:
> From: Terry Bowman <terry.bowman@....com>
> 
> ACPI includes a CXL _OSC support procedure to communicate the available
> CXL support to FW. The CXL support _OSC includes a field to indicate
> CXL1.1 RCH RCD support. The OS sets this bit to 1 if it supports access
> to RCD and RCH Port registers.[1] FW can potentially change it's operation

s/it's/its/

> depending on the _OSC support setting reported by the OS.
> 
> The ACPI driver does not currently set the ACPI _OSC support to indicate
> CXL1.1 RCD RCH support. Change the capability reported to include CXL1.1.

Eight instances of "support" above seems like it might be more than
necessary.

I don't know the history, but OSC_CXL_1_1_PORT_REG_ACCESS_SUPPORT and
OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT seem like sort of weird names
since they don't match the spec at all ("RCD and RCH Port Register
Access Supported" and "CXL VH Register Access Supported").

> [1] CXL3.0 Table 9-26 'Interpretation of CXL _OSC Support Field'
> 
> Signed-off-by: Terry Bowman <terry.bowman@....com>
> Signed-off-by: Robert Richter <rrichter@....com>
> ---
>  drivers/acpi/pci_root.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index c8385ef54c37..094a59b216ae 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -492,6 +492,7 @@ static u32 calculate_cxl_support(void)
>  	u32 support;
>  
>  	support = OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT;
> +	support |= OSC_CXL_1_1_PORT_REG_ACCESS_SUPPORT;
>  	if (pci_aer_available())
>  		support |= OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT;
>  	if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
> -- 
> 2.30.2
>