Message-ID: <6e7678ba-1d56-155f-f5b7-3257bbd0d929@redhat.com>
Date:   Tue, 15 Feb 2022 12:43:19 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>,
        Mario Limonciello <Mario.Limonciello@....com>
Cc:     linux-ide@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Nehal-bakulchandra Shah <Nehal-bakulchandra.Shah@....com>
Subject: Re: [PATCH 1/2] ahci: Add Green Sardine vendor ID as
 board_ahci_mobile

Hi all,

On 2/15/22 08:05, Paul Menzel wrote:
> Dear Mario,
> 
> 
> Am 14.02.22 um 17:07 schrieb Limonciello, Mario:
> 
>> +Hans
>>
>>> (For the records, is part of Linux since 5.16-rc2 (commit 1527f69204fe).)
>>>
>>> Am 12.11.21 um 21:15 schrieb Mario Limonciello:
>>>> AMD requires that the SATA controller be configured for devsleep in order
>>>> for S0i3 entry to work properly.
>>>>
>>>> commit b1a9585cc396 ("ata: ahci: Enable DEVSLP by default on x86 with
>>>> SLP_S0") sets up a kernel policy to enable devsleep on Intel mobile
>>>> platforms that are using s0ix.  Add the PCI ID for the SATA controller in
>>>> Green Sardine platforms to extend this policy by default for AMD based
>>>> systems using s0i3 as well.
>>>>
>>>> Cc: Nehal-bakulchandra Shah <Nehal-bakulchandra.Shah@....com>
>>>> BugLink:
>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugz
>>> illa.kernel.org%2Fshow_bug.cgi%3Fid%3D214091&amp;data=04%7C01%7Cm
>>> ario.limonciello%40amd.com%7Ca32a202d437544cd2cbb08d9ef9112c0%7C3d
>>> d8961fe4884e608e11a82d994e183d%7C0%7C0%7C637804228648002522%7CU
>>> nknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI
>>> 6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=CbfImBnwc8uV1L5QRBuV
>>> PLkP72wpS9yif1UbUwykhNI%3D&amp;reserved=0
> 
> You have to love Microsoft Outlook.
> 
>>>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>>>> ---
>>>>    drivers/ata/ahci.c | 1 +
>>>>    1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
>>>> index d60f34718b5d..1e1167e725a4 100644
>>>> --- a/drivers/ata/ahci.c
>>>> +++ b/drivers/ata/ahci.c
>>>> @@ -438,6 +438,7 @@ static const struct pci_device_id ahci_pci_tbl[] = {
>>>>        /* AMD */
>>>>        { PCI_VDEVICE(AMD, 0x7800), board_ahci }, /* AMD Hudson-2 */
>>>>        { PCI_VDEVICE(AMD, 0x7900), board_ahci }, /* AMD CZ */
>>>> +    { PCI_VDEVICE(AMD, 0x7901), board_ahci_mobile }, /* AMD Green Sardine */
>>>
>>> Aren't 0x7900 and 0x7901 the same device only in different modes? I
>>> wonder, why different boards and different comments are used.
>>
>> No they aren't the same device in different modes.
>>
>> Reference:
>> https://www.amd.com/en/support/tech-docs/processor-programming-reference-ppr-for-amd-family-19h-model-51h-revision-a1
>> Page 33 has a table.
> 
> That table misses 0x7900h. (Where can I find it?) coreboot has 0x7900 defined for Cezanne:
> 
>     src/include/device/pci_ids.h:#define PCI_DEVICE_ID_AMD_CZ_SATA  0x7900
>     src/soc/amd/stoneyridge/include/soc/pci_devs.h: * SATA_IDE_IDEVID              0x7900
> 
> The PCI database too [3]:
> 
>> FCH SATA Controller [IDE mode]
> 
> 
>>> Additionally, the device 0x7901 is also present in desktop systems like
>>> Dell OptiPlex 5055 and MSI B350 MORTAR. Is `board_ahci_mobile` the right
>>> board then? Or should the flag `AHCI_HFLAG_IS_MOBILE` be renamed to
>>> avoid confusion?
>>
>> Are you having a problem or just want clarity in the enum definition?
> 
> It’s more about clarity, and understanding the two different entries.
> 
>> This was introduced by Hans in commit ebb82e3c79d2a to set LPM policy properly
>> for a number of mobile devices.
>>
>> My opinion here is that the policy being for "mobile" devices only is short sighted as power
>> consumption policy on desktops is also relevant as OEMs ship desktops that need to meet
>> various power regulations for those too.
>>
>> So I would be in the camp for renaming the flags.
> 
> Why can’t the LPM policy, if available(?), not be set for `board_ahci` by default, so `board_ahci_mobile` could be removed?

When I added this, which was around the Haswell / Broadwell times, enabling
LPM on mobile devices was not so much important for the direct power-saving,
but to allow the entire package (integrated southbridge-ish) to go to deeper
sleep (aka PC) states.

Without this laptops would drain their batteries much faster, but at the same
time there were reports of LPM causing crashes and data corruption on some
systems, also see the list of ATA ids with a ATA_HORKAGE_NOLPM flag in
drivers/ata/libata-core.c . Which was added and grown over time to allow
enabling LPM by default without causing regressions.

So when adding support for enabling LPM modes by default, to get the
desired power-savings by default I tried to do this on a minimal set of
devices, to avoid causing regressions.

Another factor here is that in some cases LPM related issues went away
after either BIOS or disk/ssd firmware updates. So the motherboard firmware
is also a factor here and enabling LPM by default on non laptop(ish)
motherboards has never been tested.

Also enabling some of the deeper LPM modes comes at a latency cost which
may be undesirable at servers. Note this just sets the initial default
LPM mode, this can always be changed by userspace later.

Regards,

Hans





> 
>>>>        /* AMD is using RAID class only for ahci controllers */
>>>>        { PCI_VENDOR_ID_AMD, PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID,
>>>>          PCI_CLASS_STORAGE_RAID << 8, 0xffffff, board_ahci },
> 
> 
> Kind regards,
> 
> Paul
> 
> 
> [1]: https://review.coreboot.org/10418
> [2]: https://review.coreboot.org/20200
> [3]: https://pci-ids.ucw.cz/read/PC/1022/7900
> 

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