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

[Dave Jiang <dave.jiang@intel.com>]

On 2/9/23 7:02 AM, Jonathan Cameron wrote:
> 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.

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

Ok

> 
>> +
>> +	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.

Ok

> 
> 	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.

Will remove check.

> 
> 	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.

Ok will add check and warn.

> 
>> +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/.
>>
>>
>