linux-kernel - Re: [PATCH v9 4/6] Documentation: DT: PL011: hi6220: add compatible string for Hisilicon designed UART

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Message-ID: <556D73B6.4090608@arm.com>
Date:	Tue, 02 Jun 2015 10:13:26 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Linus Walleij <linus.walleij@...aro.org>,
	Bintian Wang <bintian.wang@...wei.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>
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	<linux-arm-kernel@...ts.infradead.org>,
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	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
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	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Mark Rutland <Mark.Rutland@....com>,
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Subject: Re: [PATCH v9 4/6] Documentation: DT: PL011: hi6220: add compatible
 string for Hisilicon designed UART

On 02/06/15 09:59, Linus Walleij wrote:
> On Sat, May 30, 2015 at 3:50 AM, Bintian Wang <bintian.wang@...wei.com> wrote:
> 
>> Hisilicon does some performance enhancements based on PL011(e.g. larger
>> FIFO length), so add one compatible string "hisilicon,hi6220-uart" for
> 
> That compatible string in the commit message is not even
> the same as in the patch.
> 
>> future optimisations or workarounds works.
>>
>> Signed-off-by: Bintian Wang <bintian.wang@...wei.com>
>> Suggested-by: Mark Rutland <mark.rutland@....com>
> 
> Maybe I missed out on the earlier conversation, but do you
> mean that the PrimeCell ID has not been properly set up
> to something unique in this HiSilicon version of the PL011
> block?
> 
> Even if so: do not override the compatible string like this,
> that is not the PrimeCell style.
> 
> Define an 8 bit vendor ID (like tha ASCII for 'H' 0x48
> or whatever) and encode it for these variants, if the
> hardware is just using the ARM default PrimeCell
> ID, override it in the device tree like Broadcom
> are doing in arch/arm/boot/dts/bcm2835.dtsi:
> 
> arm,primecell-periphid = <0x00241011>;
> 
> Maybe yours would be:
> 
> arm,primecell-periphid = <0x00048011>;
> 
> For a first HiSilicon variant, then do some
> <include/linux/amba/bus.h>:
> 
> enum amba_vendor {
>         AMBA_VENDOR_ARM = 0x41,
> +       AMBA_VENDOR_HISILICON = 0x48,
> 
> Then patch drivers/tty/serial/amba_pl011.c to add vendor_hisilicon
> and a match table for 0x00048011 just like everyone else.

That feels weird. This amba_vendor enum is not under control of the DT
author, nor the kernel. This is a set of codes that are managed by a
third party (probably ARM). What if some company with a name starting
with 'H' (Hilarious Inc?) comes up with some actual HW and ends up
conflicting with the above?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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