Re: [RFC] ACPI table HID/CID allocation

[Andrew Fish <afish@apple.com>]

> On Nov 25, 2017, at 4:56 AM, Udit Kumar <udit.kumar@nxp.com> wrote:
> 
> 
> 
>> -----Original Message-----
>> From: Daniel Thompson [mailto:daniel.thompson@linaro.org]
>> Sent: Thursday, November 23, 2017 1:42 AM
>> To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> Cc: Udit Kumar <udit.kumar@nxp.com>; Leif Lindholm
>> <leif.lindholm@linaro.org>; edk2-devel@lists.01.org; Varun Sethi
>> <V.Sethi@nxp.com>; Graeme Gregory <graeme.gregory@linaro.org>
>> Subject: Re: [RFC] ACPI table HID/CID allocation
>> 
> 
>>> 
>>> PRP0001 + compatible was invented to avoid the need to allocate a _HID
>>> for each and every component in existence that can already be
>>> identified by a DT compatible string (and little else except, e.g., a
>>> I2C slave address) and is not deeply engrained in the SoC in terms of
>>> clock tree, power states etc. So while internal/external may not be
>>> the most accurate distinction, it is still a useful one IMHO.
>> 
>> Hmnnn.... it sounds like jedec,spi-nor meets this test.
>> 
>> There is only one property in the DT bindings that describes the device
>> itself (fast read support) rather than its "bus address" (chip select,
>> frequency). Further, that single property is obsolete, at least for
>> Linux; the kernel driver now contains a quirks tables to look up by
>> device ID whether fast read is supported and will use that on non-DT
>> systems (and also to censor broken DT systems ;-) ).
> 
> 
> You mean, this more on bus frame work, how to probe slave. 
> Example rtc-ds3232.c , when is spi mode just need name 
> but for i2c mode it needs of_match_table
> 

Udit,

I think it is more like you only need ACPI if you don't have a driver. If it is standard bus with standard drivers the OS code can do power management without any help from ACPI. In general ACPI exists to abstract chipsets that don't have OS drivers, or mother board layout of power plains, GPIOs, etc. 

Thanks,

Andrew Fish


> Thanks 
> Udit 
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