linux-kernel - Re: [PATCH 03/10] platform/x86/intel/ifs: Image loading for new generations

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Date:   Mon, 18 Sep 2023 10:45:31 -0700
From:   "Joseph, Jithu" <jithu.joseph@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        "Luck, Tony" <tony.luck@...el.com>
CC:     Hans de Goede <hdegoede@...hat.com>,
        "markgross@...nel.org" <markgross@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Xu, Pengfei" <pengfei.xu@...el.com>
Subject: Re: [PATCH 03/10] platform/x86/intel/ifs: Image loading for new
 generations



On 9/18/2023 9:58 AM, Dave Hansen wrote:
> On 9/18/23 09:51, Joseph, Jithu wrote:
>>
>> On 9/18/2023 9:29 AM, Ilpo Järvinen wrote:
>>
>>> In this case it is not just about the bitfield itself nor the bit 
>>> allocation order but sharing the storage unit with another member, and to 
>>> further complicate things, members have different alignment requirement 
>>> too (32-bit aligned u8 followed by u32 bitfield).
>>>
>> I too verified that the size of the whole structure matches that of MSR  64 bits (8 bytes). 
>>
>> Initially when IFS scan was added the  all MSR structure members were  bit-fields, later there was a suggestion to
>> use basic C types if applicable during subsequent Array BIST patch series. I followed this approach with the  current patch series . 
>>
>> I will change the current series to use all bit-field MSR structures in v2, given mixing basic types and bitfields is a a source of confusion
> 
> That's the wrong direction. :)
> 
> What is more obviously correct.  This:
> 
> 	struct {
> 		u16	valid_chunks;
> 		u16	total_chunks;
> 		u8	error_code;
> 		u8	rsvd1;
> 		u8	rsvd2;
> 		u8	rsvd3;
> 	};
> 
> or this:
> 
> 	struct {
> 		u16	valid_chunks;
> 		u16	total_chunks;
> 		u32	error_code	:8;
> 		u32	rsvd		:24;
> 	};

I will go with the second pattern above, given that pattern can be followed for other MSR structures too, where fields doesn't split as evenly

Jithu