linux-kernel - Re: [PATCH v2 07/20] mips: Add MIPS Warrior P5600 support

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Date:   Fri, 8 May 2020 00:19:23 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
CC:     Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>, <linux-pm@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Alexander Lobakin <alobakin@...nk.ru>,
        Huacai Chen <chenhc@...ote.com>,
        Cedric Hombourger <Cedric_Hombourger@...tor.com>,
        René van Dorst <opensource@...rst.com>,
        Ard Biesheuvel <ardb@...nel.org>, Jessica Yu <jeyu@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        <linux-mips@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 07/20] mips: Add MIPS Warrior P5600 support

On Thu, May 07, 2020 at 01:17:35PM +0200, Thomas Bogendoerfer wrote:
> On Wed, May 06, 2020 at 08:42:25PM +0300, Sergey.Semin@...kalelectronics.ru wrote:
> >  
> > +config CPU_P5600
> > +	bool "MIPS Warrior P5600"
> > +	depends on SYS_HAS_CPU_P5600
> > +	select CPU_HAS_PREFETCH
> > +	select CPU_SUPPORTS_32BIT_KERNEL
> > +	select CPU_SUPPORTS_HIGHMEM
> > +	select CPU_SUPPORTS_MSA
> > +	select CPU_SUPPORTS_UNCACHED_ACCELERATED
> > +	select CPU_SUPPORTS_CPUFREQ
> > +	select CPU_MIPSR2_IRQ_VI
> > +	select CPU_MIPSR2_IRQ_EI
> > +	select HAVE_KVM
> > +	select MIPS_O32_FP64_SUPPORT
> > +	help
> > +	  Choose this option to build a kernel for MIPS Warrior P5600 CPU.
> > +	  It's based on MIPS32r5 ISA with XPA, EVA, dual/quad issue exec pipes,
> > +	  MMU with two-levels TLB, UCA, MSA, MDU core level features and system
> > +	  level features like up to six P5600 calculation cores, CM2 with L2
> > +	  cache, IOCU/IOMMU (though might be unused depending on the system-
> > +	  specific IP core configuration), GIC, CPC, virtualisation module,
> > +	  eJTAG and PDtrace.
> > +
> >  config CPU_R3000
> >  	bool "R3000"
> >  	depends on SYS_HAS_CPU_R3000
> > @@ -1841,7 +1863,8 @@ endchoice
> >  config CPU_MIPS32_3_5_FEATURES
> >  	bool "MIPS32 Release 3.5 Features"
> >  	depends on SYS_HAS_CPU_MIPS32_R3_5
> > -	depends on CPU_MIPS32_R2 || CPU_MIPS32_R5 || CPU_MIPS32_R6
> > +	depends on CPU_MIPS32_R2 || CPU_MIPS32_R5 || CPU_MIPS32_R6 || \
> > +		   CPU_P5600
> >  	help
> >  	  Choose this option to build a kernel for release 2 or later of the
> >  	  MIPS32 architecture including features from the 3.5 release such as
> > @@ -1861,7 +1884,7 @@ config CPU_MIPS32_3_5_EVA
> >  config CPU_MIPS32_R5_FEATURES
> >  	bool "MIPS32 Release 5 Features"
> >  	depends on SYS_HAS_CPU_MIPS32_R5
> > -	depends on CPU_MIPS32_R2 || CPU_MIPS32_R5
> > +	depends on CPU_MIPS32_R2 || CPU_MIPS32_R5 || CPU_P5600
> >  	help
> >  	  Choose this option to build a kernel for release 2 or later of the
> >  	  MIPS32 architecture including features from release 5 such as
> > @@ -2016,6 +2039,10 @@ config SYS_HAS_CPU_MIPS64_R6
> >  	bool
> >  	select ARCH_HAS_SYNC_DMA_FOR_CPU if DMA_NONCOHERENT
> >  
> > +config SYS_HAS_CPU_P5600
> > +	bool
> > +	select ARCH_HAS_SYNC_DMA_FOR_CPU if DMA_NONCOHERENT
> > +
> 
> P5600 is CPU_MIPS_R5 so can't you select it here and drop all the || CPU_5600
> above/below ?

Alas, We can't do this so easy. CONFIG_CPU_MIPS32_{R2,R5,R6} and any other
CONFIG_CPU_* configs is something that kernel config-file is supposed to select.
Their availability is enabled by the CONFIG_SYS_HAS_CPU_* configs. CONFIG_CPU_*
is supposed to activate CPU-specific features and there is only one
CONFIG_CPU_x can be enabled at a time seeing it's a part of the "CPU type"
choice kconfig menu. In addition the CPU config also tunes a compiler to activate
the arch-specific ISA and optimizations in the arch/mips/Makefile by setting
-march=cpu-name (where cpu-name can be p5600, mips32r5, etc).

Yes, P5600 is based on the MIPS32r5, but it also has got some specific features
(see config CPU_P5600 and config MIPS32_R5), which makes it to be different from
the ancestor. So In addition to the difficulties described above IMHO converting
CPU_P5600 to a set of features activated on top of the CPU_MIPS32_R5 config
would contradict the design of the CPU-support configs implemented in the MIPS
arch subsystem.

-Sergey

> 
> Thomas.
> 
> -- 
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]