linux-kernel - Re: [PATCH 2/4] acpi/ghes, efi/cper: Recognize and process CXL Protocol Errors.

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Date: Thu, 23 May 2024 14:19:51 -0700
From: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
To: Dave Jiang <dave.jiang@...el.com>, linux-efi@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>,
 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>,
 Yazen Ghannam <yazen.ghannam@....com>, Bowman Terry <terry.bowman@....com>
Subject: Re: [PATCH 2/4] acpi/ghes, efi/cper: Recognize and process CXL
 Protocol Errors.

Hi Dave,

On 5/22/2024 10:59 AM, Dave Jiang wrote:
> 
> 
> On 5/22/24 8:08 AM, Smita Koralahalli wrote:
>> UEFI v2.10 section N.2.13 defines a CPER record for CXL Protocol errors.
>>
>> Add GHES support to detect CXL CPER Protocol Error Record and Cache Error
>> Severity, Device ID, Device Serial number and CXL RAS capability struct in
>> struct cxl_cper_prot_err. Include this struct as a member of struct
>> cxl_cper_work_data.
>>
>> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
>> ---
>>   drivers/acpi/apei/ghes.c        | 10 +++++
>>   drivers/firmware/efi/cper_cxl.c | 66 +++++++++++++++++++++++++++++++++
>>   include/linux/cxl-event.h       | 26 +++++++++++++
>>   3 files changed, 102 insertions(+)
>>

[snip]


>> +	 * The device ID or agent address is required for CXL RCD, CXL
>> +	 * SLD, CXL LD, CXL Fabric Manager Managed LD, CXL Root Port,
>> +	 * CXL Downstream Switch Port and CXL Upstream Switch Port.
>> +	 */
>> +	if (prot_err->agent_type <= 0x7 && prot_err->agent_type != RCH_DP) {
> 
> Perhaps define an enum CXL_AGENT_TYPE_MAX instead of 0x7 magic number? Otherwise if a new type is introduced, it would break this code.

Agreed. I will define a boolean array indexed by agent type as suggested 
by Alison. That would avoid all these comparisons and not worry about 
breaking code in future.

>   
>> +		p_err->segment = prot_err->agent_addr.segment;
>> +		p_err->bus = prot_err->agent_addr.bus;
>> +		p_err->device = prot_err->agent_addr.device;
>> +		p_err->function = prot_err->agent_addr.function;
>> +	} else {
>> +		pr_err(FW_WARN "Invalid agent type\n");
>> +		return -EINVAL;
>> +	}
> 
> Up to you if you want to do this or not, but maybe:
> 
> 	if (prot_err->agent_type >= CXL_AGENT_TYPE_MAX || prot_err->agent_type == RCH_DP) {
> 		pr_warn(...);
> 		return -EINVAL;
> 	}
> 
> 	p_err->segment = ...;
> 	p_err->bus = ...;

Noted.

> 	...
> 
> Although perhaps a helper function cxl_cper_valid_agent_type() that checks invalid agent type by checking the valid_bits, the agent_type boundary, and if agent_type != RCH_DP?

Okay.

>> +
>> +	if (!(prot_err->valid_bits & PROT_ERR_VALID_ERROR_LOG)) {
>> +		pr_err(FW_WARN "Invalid Protocol Error log\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	dvsec_start = (u8 *)(prot_err + 1);
>> +	cap_start = dvsec_start + prot_err->dvsec_len;
>> +	p_err->cxl_ras = *(struct cxl_ras_capability_regs *)cap_start;
>> +
>> +	/*
>> +	 * Set device serial number unconditionally.
>> +	 *
>> +	 * Print a warning message if it is not valid. The device serial
>> +	 * number is required for CXL RCD, CXL SLD, CXL LD and CXL Fabric
>> +	 * Manager Managed LD.
>> +	 */
>> +	if (!(prot_err->valid_bits & PROT_ERR_VALID_SERIAL_NUMBER) ||
>> +	      prot_err->agent_type > 0x4 || prot_err->agent_type == RCH_DP)
> 
> prot_err->agent_type > FM_LD? Although maybe it would be a clearer read if a helper function is defined to identify the agent types such as cxl_cper_prot_err_serial_needed() or cxl_cper_prot_agent_type_device() and with it a switch statement to explicitly identify all the agent types that require serial number. If a future device is defined, the > 0x4 logic may break.

Probably helper function is not required if boolean array is defined? 
What do you think?

Thanks,
Smita

[snip]