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

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2015/12/3 23:56, Lorenzo Pieralisi wrote:
> 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 ?

SAS： https://lkml.org/lkml/2015/11/17/572
      [PATCH v5 19/32] scsi: hisi_sas: add v1 HW initialisation code
      static int reset_hw_v1_hw(struct hisi_hba *hisi_hba);

HNS： drivers/net/ethernet/hisilicon/hns_mdio.c
      static int hns_mdio_reset(struct mii_bus *bus)；

> 
>> 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 ?

This is unrelated to reset control.

I mean we have some driver(not upstreamed), like LLC(last level cache), when access the register
of llc, we need help through syscon, because the llc has no independent registers region , steps
of Read and Write register in those drivers is shown below,

 1) get the syscon base;
 2) configure and choose the module which need to be accessed;
 3) R/W the value from the syscon, that is, get/set the value from/to llc;

Every read and write the register in those drivers, we must through syscon. That is why we need
syscon to support ACPI.

Thanks,
Kefeng


> 
> 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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