Re: [PATCH 08/18] cxl: Add support for _DSM Function for retrieving QTG ID

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Mon, 06 Feb 2023 13:50:33 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> CXL spec v3.0 9.17.3 CXL Root Device Specific Methods (_DSM)
> 
> Add support to retrieve QTG ID via ACPI _DSM call. The _DSM call requires
> an input of an ACPI package with 4 dwords (read latency, write latency,
> read bandwidth, write bandwidth). The call returns a package with 1 WORD
> that provides the max supported QTG ID and a package that may contain 0 or
> more WORDs as the recommended QTG IDs in the recommended order.
> 
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
A few minor bits inline.

Jonathan

> ---
>  drivers/cxl/core/Makefile |    1 
>  drivers/cxl/core/acpi.c   |   99 +++++++++++++++++++++++++++++++++++++++++++++
>  drivers/cxl/cxl.h         |   15 +++++++
>  3 files changed, 115 insertions(+)
>  create mode 100644 drivers/cxl/core/acpi.c
> 
> diff --git a/drivers/cxl/core/Makefile b/drivers/cxl/core/Makefile
> index 438ce27faf77..11ccc2016ab7 100644
> --- a/drivers/cxl/core/Makefile
> +++ b/drivers/cxl/core/Makefile
> @@ -11,4 +11,5 @@ cxl_core-y += mbox.o
>  cxl_core-y += pci.o
>  cxl_core-y += hdm.o
>  cxl_core-y += cdat.o
> +cxl_core-y += acpi.o
>  cxl_core-$(CONFIG_CXL_REGION) += region.o
> diff --git a/drivers/cxl/core/acpi.c b/drivers/cxl/core/acpi.c
> new file mode 100644
> index 000000000000..86dc6c9c1f24
> --- /dev/null
> +++ b/drivers/cxl/core/acpi.c
> @@ -0,0 +1,99 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright(c) 2022 Intel Corporation. All rights reserved. */
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/acpi.h>
> +#include <linux/pci.h>
> +#include <asm/div64.h>
> +#include "cxlpci.h"
> +#include "cxl.h"
> +
> +const guid_t acpi_cxl_qtg_id_guid =
> +	GUID_INIT(0xF365F9A6, 0xA7DE, 0x4071,
> +		  0xA6, 0x6A, 0xB4, 0x0C, 0x0B, 0x4F, 0x8E, 0x52);
> +
> +/**
> + * cxl_acpi_evaluate_qtg_dsm - Retrieve QTG ids via ACPI _DSM
> + * @handle: ACPI handle
> + * @input: bandwidth and latency data
> + *
> + * Issue QTG _DSM with accompanied bandwidth and latency data in order to get
> + * the QTG IDs that falls within the performance data.
> + */
> +struct qtg_dsm_output *cxl_acpi_evaluate_qtg_dsm(acpi_handle handle,
> +						 struct qtg_dsm_input *input)
> +{
> +	struct qtg_dsm_output *output;
> +	union acpi_object *out_obj, *out_buf, *pkg, in_buf, in_obj;

Reorder to reverse Xmas tree perhaps.

> +	int len;
> +	int rc;
Might as well put those on one line.

> +
> +	in_obj.type = ACPI_TYPE_PACKAGE;
> +	in_obj.package.count = 1;
> +	in_obj.package.elements = &in_buf;
> +	in_buf.type = ACPI_TYPE_BUFFER;
> +	in_buf.buffer.pointer = (u8 *)input;
> +	in_buf.buffer.length = sizeof(u32) * 4;
c99 style is nicer to read.

	union acpi_object in_obj = {
		.type = 

	}
> +
> +	out_obj = acpi_evaluate_dsm(handle, &acpi_cxl_qtg_id_guid, 1, 1, &in_obj);
> +	if (!out_obj)
> +		return ERR_PTR(-ENXIO);
> +
> +	if (out_obj->type != ACPI_TYPE_PACKAGE) {
> +		rc = -ENXIO;
> +		goto err;
> +	}
> +
> +	/*
> +	 * CXL spec v3.0 9.17.3.1
> +	 * There should be 2 elements in the package. 1 WORD for max QTG ID supported
> +	 * by the platform, and the other a package of recommended QTGs
> +	 */
> +	if (out_obj->package.count != 2) {

This stuff is usually designed to be extensible - tends to be explicitly allowed in
stuff in the ACPI spec (not mentioned AFAICT in the CXL spec).  So I'd be tempted to allow
> 2 just don't read them.

	if (out_obj->package.count < 2) {
> +		rc = -ENXIO;
> +		goto err;
> +	}
> +
> +	pkg = &out_obj->package.elements[1];
> +	if (pkg->type != ACPI_TYPE_PACKAGE) {
> +		rc = -ENXIO;
> +		goto err;
> +	}
> +
> +	out_buf = &pkg->package.elements[0];
> +	if (out_buf->type != ACPI_TYPE_BUFFER) {
> +		rc = -ENXIO;
> +		goto err;
> +	}
> +
> +	len = out_buf->buffer.length;
> +	output = kmalloc(len + sizeof(*output), GFP_KERNEL);
> +	if (!output) {
> +		rc = -ENOMEM;
> +		goto err;
> +	}
> +
> +	/* It's legal to have 0 QTG entries */
> +	if (len == 0) {
> +		output->nr = 0;
> +		goto out;
> +	}
> +
> +	/* Malformed package, not multiple of WORD size */
> +	if (len % sizeof(u16)) {
> +		rc = -ENXIO;
> +		goto out;
> +	}
> +
> +	output->nr = len / sizeof(u16);
> +	memcpy(output->qtg_ids, out_buf->buffer.pointer, len);

Worth checking them against Max Support QTG ID as provided in the
outer package?  Obviously if they are greater than that there is
a bug, but meh.

> +out:
> +	ACPI_FREE(out_obj);
> +	return output;
> +
> +err:
> +	ACPI_FREE(out_obj);
> +	return ERR_PTR(rc);
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_acpi_evaluate_qtg_dsm, CXL);
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 849b22236f1d..e70df07f9b4b 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -719,6 +719,21 @@ int cdat_table_parse_dslbis(void *table, cdat_tbl_entry_handler handler,
>  int cxl_dsmas_parse_entry(struct acpi_cdat_header *header, void *arg);
>  int cxl_dslbis_parse_entry(struct acpi_cdat_header *header, void *arg);
>  
> +struct qtg_dsm_input {
> +	u32 rd_lat;
> +	u32 wr_lat;
> +	u32 rd_bw;
> +	u32 wr_bw;
> +};
> +
> +struct qtg_dsm_output {
> +	int nr;
> +	u16 qtg_ids[];
> +};
> +
> +struct qtg_dsm_output *cxl_acpi_evaluate_qtg_dsm(acpi_handle handle,
> +						 struct qtg_dsm_input *input);
> +
>  /*
>   * Unit test builds overrides this to __weak, find the 'strong' version
>   * of these symbols in tools/testing/cxl/.
> 
>