linux-kernel - Re: [PATCH 12/14] platform/x86/intel/ifs: Add current

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Date:   Tue, 1 Nov 2022 16:27:12 -0700
From:   "Joseph, Jithu" <jithu.joseph@...el.com>
To:     Sohil Mehta <sohil.mehta@...el.com>, <hdegoede@...hat.com>,
        <markgross@...nel.org>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
        <gregkh@...uxfoundation.org>, <ashok.raj@...el.com>,
        <tony.luck@...el.com>, <linux-kernel@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>, <patches@...ts.linux.dev>,
        <ravi.v.shankar@...el.com>, <thiago.macieira@...el.com>,
        <athenas.jimenez.gonzalez@...el.com>
Subject: Re: [PATCH 12/14] platform/x86/intel/ifs: Add current_batch sysfs
 entry



On 11/1/2022 3:26 PM, Sohil Mehta wrote:
> On 10/21/2022 1:34 PM, Jithu Joseph wrote:
>> Initial implementation assumed a single IFS test image file with a
>> fixed name ff-mm-ss.scan. (where ff, mm, ss refers to family, model
>> and stepping  of the core)
>>
>> Subsequently, it became evident that supporting more than one
>> test image file is needed to provide more comprehensive
>> test coverage. (Test coverage in this scenario refers to testing
>> more transistors in the core to identify faults)
>>
>> The other alternative of increasing the size of a single scan test image
>> file would not work as the  upper bound is limited by the size of memory
>> area reserved by BIOS for loading IFS test image.
>>
>> Introduce "current_batch" file which accepts a number. Writing a
>> number to the current_batch file would load the test image file by name
>> ff-mm-ss-<xy>.scan, where <xy> is the number written to the
>> "current_batch" file in hex. 
> 
> Any specific reasoning why the name "current_batch" was chosen? To me, batch seems to suggest multiple or a group of files. But in reality only one test file is loaded at a time.

There would be a batch of test files (6 in the e.g described in the commit message). At a time you can load one by writing its suffix into "current_batch". So "current_batch" was more like a short form for "current_file_in_the_batch_of_files"

> 
> Naming can sometimes be quite subjective so it might be useful to get multiple opinions here.
> 
> As per my understanding, there is sysfs file called run_test which runs a loaded test. Instead of current_batch how about the name load_test (or maybe current_test)?

Each file would contain multiple tests. All these tests contained within a file would be executed when you write 1 to "runtest".
Given this load_test too would be confusing (more appropriate than "load_test" would be "load_test_file" or "load_file" or "current_file")

> 
> load_test - Write a number less than or equal to 0xff to load an IFS test image. (Description as-is from the documentation patch)
> 
> 
>>    * Running tests
>>    * -------------
>> @@ -207,6 +217,7 @@ struct ifs_data {
>>       int    status;
>>       u64    scan_details;
>>       int    cur_batch;
>> +    int    test_num;
>>   };
>>     struct ifs_work {
>> diff --git a/drivers/platform/x86/intel/ifs/core.c b/drivers/platform/x86/intel/ifs/core.c
>> index 5fb7f655c291..1f040837e8eb 100644
>> --- a/drivers/platform/x86/intel/ifs/core.c
>> +++ b/drivers/platform/x86/intel/ifs/core.c
>> @@ -22,6 +22,7 @@ MODULE_DEVICE_TABLE(x86cpu, ifs_cpu_ids);
>>   static struct ifs_device ifs_device = {
>>       .data = {
>>           .integrity_cap_bit = MSR_INTEGRITY_CAPS_PERIODIC_BIST_BIT,
>> +        .test_num = 0,
> 
> Is this initialization really needed? Wouldn't it default to 0?
> 

Not strictly needed when we have a single test

> Maybe if you explain what does test_num refer to it might answer the above?

It is currently used to form the path in ifs_load_firmware() for the test image to be loaded

> 
> 
>> +static ssize_t current_batch_show(struct device *dev,
>> +                  struct device_attribute *attr, char *buf)
>> +{
>> +    struct ifs_data *ifsd = ifs_get_data(dev);
>> +
>> +    if (!ifsd->loaded)
>> +        return sysfs_emit(buf, "%s\n", "none");
> 
> Why not:
> 
> sysfs_emit(buf, "none\n");

Will change

Jithu