[RFC PATCH 4/4] mfd: syscon: add ACPI support

From: lorenzo.pieralisi@arm.com (Lorenzo Pieralisi)
To: linux-arm-kernel@lists.infradead.org
Subject: [RFC PATCH 4/4] mfd: syscon: add ACPI support
Date: Thu, 3 Dec 2015 15:56:12 +0000	[thread overview]
Message-ID: <20151203155612.GA2935@red-moon> (raw)
In-Reply-To: <56603D17.4080707@huawei.com>

On Thu, Dec 03, 2015 at 09:01:11PM +0800, Kefeng Wang wrote:
> Hi Graeme, Arnd, and Lorenzo,
> 
> Firstly, we absolutely agree with the point which use AML to do some "special"
> initialisation and configuration.

Good.

> SAS and NIC driver were accepted by linux in hisilicon hip05 chip, and the drivers
> reset the control by syscon, we want to use "_RST" method, which is introduced by
> ACPI 6.0 spec in "7.3.25 _RST (Device Reset)", is it reasonable and standard for us?

Can you point me at the drivers you are referring to please ?

> But here is a scene, we can not find a suitable way to support ACPI. There is no
> independent memory region in some module(the driver not upstreamed), that is,
> when write and read the module's register, we must r/w by syscon. Any advice?

What do you mean ? You mean that the reset control is a piece of HW
that is shared between multiple "components" ? What's your concern
about AML code driving those registers here ?

Thanks,
Lorenzo

> 
> Thanks,
> Kefeng
> 
> On 2015/12/3 18:41, Graeme Gregory wrote:
> > On Wed, Dec 02, 2015 at 11:44:51AM +0100, Arnd Bergmann wrote:
> >> On Wednesday 02 December 2015 17:09:28 Kefeng Wang wrote:
> >>> This enables syscon with ACPI support.
> >>> syscon_regmap_lookup_by_dev_property() function was added. With helper
> >>> device_get_reference_node() and acpi_dev_find_plat_dev(), it can be used
> >>> in both DT and ACPI.
> >>>
> >>> The device driver can obtain syscon using _DSD method in DSDT, an example
> >>> is shown below.
> >>>
> >>>     Device(CTL0) {
> >>>           Name(_HID, "HISI0061")
> >>>           Name(_CRS, ResourceTemplate() {
> >>>                   Memory32Fixed(ReadWrite, 0x80000000, 0x10000)
> >>>           })
> >>>     }
> >>>
> >>>     Device(DEV0) {
> >>>           Name(_HID, "HISI00B1")
> >>>           Name(_CRS, ResourceTemplate() {
> >>>                   Memory32Fixed(ReadWrite, 0x8c030000, 0x10000)
> >>>                   Interrupt(ResourceConsumer, Level, ActiveHigh, Exclusive){ 192 }
> >>>           })
> >>>
> >>>           Name (_DSD, Package () {
> >>>               ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> >>>               Package () {
> >>>                   Package () {"syscon",Package() {\_SB.CTL0} }
> >>>               }
> >>>           })
> >>>     }
> >>>
> >>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> >>
> >> This sounds like a bad idea:
> >>
> >> syscon is basically a hack to let us access register that the SoC designer
> >> couldn't fit in anywhere sane. We need something like this with devicetree
> >> because we decided not to have any interpreted bytecode to do this behind
> >> our back.
> >>
> >> With ACPI, the same thing is done with AML, which is actually nicer than
> >> syscon (once you have to deal with all the problems introduced by AML).
> >>
> >> Use that instead.
> >>
> > 
> > I have to agree with Arnd here, this is specifically why it was chosen
> > to use ACPI on machines to move all these "hacks" to AML.
> > 
> > This leaves your driver being generic and any "special" initialisation
> > can be supplied by the OEM through the ACPI tables.
> > 
> > Graeme
> > 
> > 
> > .
> > 
> 
> 
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