Re: [PATCH] mmc: sdhci-acpi: set non-removable in ACPI table
From: Rafael J. Wysocki
Date: Tue Dec 15 2015 - 20:17:42 EST
On 12/15/2015 10:36 PM, Philip Elcan wrote:
On 12/11/2015 05:53 PM, Rafael J. Wysocki wrote:
On Friday, December 11, 2015 10:17:18 AM Adrian Hunter wrote:
On 10/12/15 22:57, Philip Elcan wrote:
On 12/07/2015 03:30 AM, Adrian Hunter wrote:
On 04/12/15 17:40, Philip Elcan wrote:
On 12/03/2015 09:14 AM, Adrian Hunter wrote:
On 03/12/15 15:48, Philip Elcan wrote:
This allows setting an SDHC controller as non-removable
by using the _RMV method in the ACPI table. It doesn't
Is that _RMV on the host controller? Shouldn't it be on the card i.e. child
device node?
Yes, this is on the host controller. The ACPI table only describes the
host controller, not the child nodes.
If you look at Intel devices, the _RMV is on the child e.g.
Device (SDHA)
{
Name (_HID, "80860F14") // _HID: Hardware ID
Name (_CID, "PNP0D40") // _CID: Compatible ID
Name (_DDN, "Intel(R) eMMC Controller - 80860F14") // _DDN: DOS Device Name
...
Device (EMMD)
{
...
Method (_RMV, 0, NotSerialized) // _RMV: Removal Status
{
Return (Zero)
}
}
}
I am not an ACPI expert but that seems like the correct place for it.
My understanding is that in ACPI you don't generally create child devices on buses that are discoverable.
I've cc'ed Rafael and the linux-acpi mailing list. Maybe someone there can
comment.
The context here is a bit unclear to me.
Quite frankly, I don't see now _RMV above is useful for anything. As per the
spec, _RMV is only necessary for devices that *can* be removed from the system
and where there's no eject mechanism controlled by software. For those
devices _RMV is intended to indicate that it is safe to remove the device
at the time _RMV is evaluated. Devices that can never be removed don't
need _RMV at all.
Thanks,
Rafael
Maybe I'm misinterpreting something, but the spec says that "_RMV object indicates
to OSPM whether the device can be removed while the system is in the working state
and does not require any ACPI system firmware actions to be performed for the device
to be safely removed from the system." That sounds exactly like what I'm trying to
do. And from Adrian's example, it sounds like others are using this to indicate if
a devices is removeable.
It also says "Any such removable device that does not have _LCK or _EJx
control methods must have and _RMV object."
Which clearly implies that _RMV is not required for devices that cannot
be removed at all. Indeed, it is redundant in those cases as stated above.
However, if I follow your paradigm, I can just test if the _RMV object exists, and if
it doesn't, I can assume the device is not removable?
That's correct as far as I can say.
I'm concerned not all firmware will have this object implemented.
That's correct too.
It only is intended for devices that may be removed in a
surprise-removal fashion and it is rarely used in general.
Is there something else you suggest I use in the ACPI table to designate an SD/MMC
device is removable?
If you want to say "this device is removable", then there should be
either _LCK/_EJx or _RMV object present for it. The latter indicates
that the device can be removed at any time in principle, but it is only
safe to remove it if/when 1 is returned by _RMV. That is, the OS can't
prevent the user from removing the device, but it can indicate to the
user (this way or another) when it is safe to remove it. The decision
whether or not to do that is still up to the user.
Thanks,
Rafael
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/