linux-kernel - Re: [PATCH 17/27] sparc32: Drop run-time patching of ASI instructions

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Message-ID: <d1a616f1-0fd2-4af0-8b89-e0d0a8842a6d@gaisler.com>
Date: Fri, 16 Feb 2024 18:12:08 +0100
From: Andreas Larsson <andreas@...sler.com>
To: sam@...nborg.org, "David S. Miller" <davem@...emloft.net>,
 Arnd Bergmann <arnd@...nel.org>
Cc: Helge Deller <deller@....de>, Alexander Viro <viro@...iv.linux.org.uk>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Alan Stern <stern@...land.harvard.edu>, Jaroslav Kysela <perex@...ex.cz>,
 Takashi Iwai <tiwai@...e.com>, sparclinux@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
 linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-sound@...r.kernel.org
Subject: Re: [PATCH 17/27] sparc32: Drop run-time patching of ASI instructions

On 2023-12-19 23:03, Sam Ravnborg via B4 Relay wrote:
> From: Sam Ravnborg <sam@...nborg.org>
> 
> With only LEON supported there is no need to run-time patch
> the instructions to match ASI.
> 
> Move a few functions back to C with inline asm, now that
> run-time patching is not needed.
> 
> Deleted a few functions that turns out not to be used rather
> than re-implement them in C.
..
> diff --git a/arch/sparc/include/asm/sections.h b/arch/sparc/include/asm/sections.h
> index 08f833453ab3..e9d28148850b 100644
> --- a/arch/sparc/include/asm/sections.h
> +++ b/arch/sparc/include/asm/sections.h
> @@ -8,7 +8,4 @@
>  /* sparc entry point */
>  extern char _start[];
>  
> -extern char __leon_1insn_patch[];
> -extern char __leon_1insn_patch_end[];
> -
>  #endif
> diff --git a/arch/sparc/include/asm/winmacro.h b/arch/sparc/include/asm/winmacro.h
> index b6e911f5d93c..c496b04cdfaf 100644
> --- a/arch/sparc/include/asm/winmacro.h
> +++ b/arch/sparc/include/asm/winmacro.h
> @@ -108,18 +108,11 @@
>  661:	rd	%tbr, %idreg;				\
>  	srl	%idreg, 10, %idreg;			\
>  	and	%idreg, 0xc, %idreg;			\

These three lines, including the label, should also be removed as they
are not for LEON. Additionally, I think it would be best to split out
removing the cpuid instruction fixups to one patch and the MMU ASI
instruction fixups to another patch.

> -	.section	.cpuid_patch, "ax";		\
> -	/* Instruction location. */			\
> -	.word		661b;				\
> -	/* SUN4D implementation. */			\
> -	lda	 [%g0] ASI_M_VIKING_TMP1, %idreg;	\
> -	sll	 %idreg, 2, %idreg;			\
> -	nop;						\
> -	/* LEON implementation. */			\
> +							\
>  	rd 	%asr17, %idreg;				\
>  	srl	%idreg, 0x1c, %idreg;			\
>  	sll	%idreg, 0x02, %idreg;			\
> -	.previous;					\
> +							\
>  	sethi    %hi(current_set), %dest_reg; 		\
>  	or       %dest_reg, %lo(current_set), %dest_reg;\
>  	ld       [%idreg + %dest_reg], %dest_reg;
> diff --git a/arch/sparc/kernel/entry.S b/arch/sparc/kernel/entry.S
> index 0f2417ee3f95..9cf8f87e8c42 100644
> --- a/arch/sparc/kernel/entry.S
> +++ b/arch/sparc/kernel/entry.S

The hard_smp_processor_id function also needs to be reduced to just the
LEON code. With the patching removed, SMP otherwise breaks with CPUs
other than CPU 0 getting stuck.

Thanks,
Andreas