Re: [RFC] ACPI table HID/CID allocation

[Daniel Thompson <daniel.thompson@linaro.org>]

On 25/11/17 12:56, Udit Kumar 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 Further, that single property is obsolete, at least for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
I mean nothing more or less than that PRP0001 + compatible:jedec,spi-nor 
is tolerable within the ACPI tables (rather than allocating a HID) 
because it has no properties[1] beyond the bus configuration that ACPI 
can already describe

I'm afraid I don't understand how rtc-ds3232.c fits into this topic; 
there are no documented device tree bindings for the SPI variant of this 
part and, in any case, an RTC should use the ACPI interfaces 
(rtc-cmos.c) so the choice HID is a moot point; it should not be in the 
ACPI tables at all.


Daniel.


[1] Assuming one accepts the argument that the m25p,fast-read property
     can be ignored.
     ignored.