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From: Mike Travis <mike.travis@hpe.com>
To: Sasha Levin <sashal@kernel.org>, Greg KH <gregkh@linuxfoundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>,
	Christoph Hellwig <hch@infradead.org>,
	Dimitri Sivanich <dimitri.sivanich@hpe.com>,
	Russ Anderson <russ.anderson@hpe.com>,
	Hedi Berriche <hedi.berriche@hpe.com>,
	Steve Wahl <steve.wahl@hpe.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org
Subject: Re: [PATCH 6/8] x86/platform/uv: Decode UVsystab Info
Date: Thu, 5 Sep 2019 15:42:41 -0700	[thread overview]
Message-ID: <9745d473-e4bc-7ae2-fc67-a898c3606088@hpe.com> (raw)
In-Reply-To: <20190905214030.GE1616@sasha-vm>



On 9/5/2019 2:40 PM, Sasha Levin wrote:
> On Thu, Sep 05, 2019 at 04:16:34PM +0200, Greg KH wrote:
>> On Thu, Sep 05, 2019 at 08:02:58AM -0500, Mike Travis wrote:
>>> --- linux.orig/arch/x86/kernel/apic/x2apic_uv_x.c
>>> +++ linux/arch/x86/kernel/apic/x2apic_uv_x.c
>>> @@ -1303,7 +1303,8 @@ static int __init decode_uv_systab(void)
>>>      struct uv_systab *st;
>>>      int i;
>>>
>>> -    if (uv_hub_info->hub_revision < UV4_HUB_REVISION_BASE)
>>> +    /* Select only UV4 (hubbed or hubless) and higher */
>>> +    if (is_uv_hubbed(-2) < uv(4) && is_uv_hubless(-2) < uv(4))
> 
> For someone not too familiar with the code, this is completely
> unreadable. There must be a nicer way to do this.
> 
> -- 
> Thanks,
> Sasha

Hi Sasha,

I can put in further explanation but first the uv() function returns 1 
left shifted by the UV #:

static inline int uv(int uvtype)
{
         /* uv(0) is "any" */
         if (uvtype >= 0 && uvtype <= 30)
                 return 1 << uvtype;
         return 1;
}

The "is_uv_hubbed(x)" and "is_uv_hubless(x)" AND's the incoming arg with 
the actual uv type:

int is_uv_hubbed(int uvtype)
{
         return (uv_hubbed_system & uvtype);
}

The uv_hub{bed,less}_system is set to 1 left shifted by the UV # plus in 
bit 0 is a '1' to indicate "any" UV (as in "is_uv_hubbed(1)" is any UV 
hubbed system).  Hubbed indicates a hubbed system, and hubless indicates 
a hubless system, it cannot be both but can be neither.

>                 /* UV4 Hubless, (0x11:UV4+Any) */
>                 if (strncmp(oem_id, "NSGI4", 5) == 0)
>                         uv_hubless_system = 0x11;
> 
>                 /* UV3 Hubless, UV300/MC990X w/o hub (0x9:UV3+Any) */
>                 else
>                         uv_hubless_system = 0x9;
> 

(There are only hubbed versions of UV1 and UV2.)

Lastly (-2) translates to 0xffff...fffe (note bit 0 is clear to avoid 
the "any" bit.   So it is looking for a a hubbed or hubless UV system 
that is less than UV4 meaning only UV4,5,6...qualify, hence this comment:

 >>> +    /* Select only UV4 (hubbed or hubless) and higher */
	if (UV is less than UV4 either hubbed or hubless)
		return;  /* does not have an extended UVsystab */

Have you a suggestion on what would make it more clear?  Perhaps instead 
of -2 I should use a hex mask?

Thanks,
Mike



  reply	other threads:[~2019-09-05 22:42 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-05 13:02 [PATCH 0/8] x86/platform/UV: Update UV Hubless System Support Mike Travis
2019-09-05 13:02 ` [PATCH 1/8] x86/platform/uv: Save OEM_ID from ACPI MADT probe Mike Travis
2019-09-05 13:02 ` [PATCH 2/8] x86/platform/uv: Return UV Hubless System Type Mike Travis
2019-09-05 13:02 ` [PATCH 3/8] x86/platform/uv: Add return code to UV BIOS Init function Mike Travis
2019-09-05 13:02 ` [PATCH 4/8] x86/platform/uv: Setup UV functions for Hubless UV Systems Mike Travis
2019-09-05 13:02 ` [PATCH 5/8] x86/platform/uv: Add UV Hubbed/Hubless Proc FS Files Mike Travis
2019-09-05 13:02 ` [PATCH 6/8] x86/platform/uv: Decode UVsystab Info Mike Travis
2019-09-05 14:16   ` Greg KH
2019-09-05 14:47     ` Mike Travis
2019-09-05 16:43       ` Mike Travis
2019-09-05 16:57         ` Greg KH
2019-09-05 16:56       ` Greg KH
2019-09-05 21:40     ` Sasha Levin
2019-09-05 22:42       ` Mike Travis [this message]
2019-09-05 13:02 ` [PATCH 7/8] x86/platform/uv: Check EFI Boot to set reboot type Mike Travis
2019-09-05 13:03 ` [PATCH 8/8] x86/platform/uv: Account for UV Hubless in is_uvX_hub Ops Mike Travis
2019-09-10 12:07 ` [PATCH 0/8] x86/platform/UV: Update UV Hubless System Support Miguel Ojeda
2019-09-10 15:34   ` Mike Travis
2019-09-10 16:40     ` Borislav Petkov
2019-09-10 16:57       ` Mike Travis
  -- strict thread matches above, loose matches on Subject: below --
2019-09-05 18:47 Mike Travis
2019-09-05 18:47 ` [PATCH 6/8] x86/platform/uv: Decode UVsystab Info Mike Travis
2019-09-03  0:18 [PATCH 0/8] x86/platform/UV: Update UV Hubless System Support Mike Travis
2019-09-03  0:18 ` [PATCH 6/8] x86/platform/uv: Decode UVsystab Info Mike Travis
2019-09-03  6:22   ` Greg KH

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