linux-kernel - Re: [PATCH V3] ACPI: Add _DEP(Operation Region Dependencies) support to fix battery issue on the Asus T100TA

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Date:	Tue, 25 Nov 2014 02:16:32 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:	Lan Tianyu <tianyu.lan@...el.com>, lenb@...nel.org,
	wsa@...-dreams.de, robert.moore@...el.com, lv.zheng@...el.com,
	shigorin@...il.com, adamw@...pyassassin.net, jan.brummer@...os.org,
	mika.westerberg@...ux.intel.com, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
	devel@...ica.org
Subject: Re: [PATCH V3] ACPI: Add _DEP(Operation Region Dependencies) support to fix battery issue on the Asus T100TA

On Tuesday, November 25, 2014 08:18:34 AM Li, Aubrey wrote:
> On 2014/11/24 23:27, Rafael J. Wysocki wrote:
> > On Monday, November 24, 2014 10:39:55 AM Li, Aubrey wrote:
> >> On 2014/11/23 21:22, Lan Tianyu wrote:
> >>> ACPI 5.0 introduces _DEP to designate device objects that OSPM should
> >>> assign a higher priority in start ordering due to future operation region
> >>> accesses.
> >>>
> >>> On Asus T100TA, ACPI battery info are read from a I2C slave device via
> >>> I2C operation region. Before I2C operation region handler is installed,
> >>> battery _STA always returns 0. There is a _DEP method of designating
> >>> start order under battery device node.
> >>>
> >>> This patch is to implement _DEP feature to fix battery issue on the Asus T100TA.
> >>> Introducing acpi_dep_list and adding dep_unmet count in the struct
> >>> acpi_device. During ACPI namespace scan, create struct acpi_dep_data for a
> >>> valid pair of master (device pointed to by _DEP)/slave(device with _DEP), record
> >>> master's and slave's ACPI handle in it and put it into acpi_dep_list. The dep_unmet
> >>> count will increase by one if there is a device under its _DEP. Driver's probe() should
> >>> return EPROBE_DEFER when find dep_unmet is larger than 0. When I2C operation
> >>> region handler is installed, remove all struct acpi_dep_data on the acpi_dep_list
> >>> whose master is pointed to I2C host controller and decrease slave's dep_unmet.
> >>> When dep_unmet decreases to 0, all _DEP conditions are met and then do acpi_bus_attach()
> >>> for the device in order to resolve battery _STA issue on the Asus T100TA.
> >>
> >> Well, Can we explicitly tied this up with ASUS T100TA in the code?
> >> If I understand correctly, the assumption in the patch is that the
> >> battery device only depends on I2C device, which is true on ASUS T100TA,
> >> but may not on the other platforms.
> >>
> >> This patch does not work on a box I have, on it _DEP contains I2C and GPIO.
> > 
> > Does the patch break anything for you?
> 
> Not I'm aware so far.

OK

It is not a complete solution, but it is an improvement.  It evidently helps
people.

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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