linux-kernel - Re: [RFC PATCH] powerpc: Convert ____flush_dcache_icache

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Message-ID: <a0ad8dd8-2f5d-256d-9e88-e9c236335bb8@c-s.fr>
Date:   Wed, 21 Aug 2019 22:27:04 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Alastair D'Silva <alastair@....ibm.com>,
        Segher Boessenkool <segher@...nel.crashing.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH] powerpc: Convert ____flush_dcache_icache_phys() to C



Le 20/08/2019 à 06:36, Alastair D'Silva a écrit :
> On Fri, 2019-08-16 at 15:52 +0000, Christophe Leroy wrote:

[...]

> 
> 
> Thanks Christophe,
> 
> I'm trying a somewhat different approach that requires less knowledge
> of assembler. Handling of CPU_FTR_COHERENT_ICACHE is outside this
> function. The code below is not a patch as my tree is a bit messy,
> sorry:

Can we be 100% sure that GCC won't add any code accessing some global 
data or stack while the Data MMU is OFF ?

Christophe


> 
> /**
>   * flush_dcache_icache_phys() - Flush a page by it's physical address
>   * @addr: the physical address of the page
>   */
> static void flush_dcache_icache_phys(unsigned long addr)
> {
> 	register unsigned long msr;
> 	register unsigned long dlines = PAGE_SIZE >> l1_dcache_shift();
> 	register unsigned long dbytes = l1_dcache_bytes();
> 	register unsigned long ilines = PAGE_SIZE >> l1_icache_shift();
> 	register unsigned long ibytes = l1_icache_bytes();
> 	register unsigned long i;
> 	register unsigned long address = addr;
> 
> 	/*
> 	 * Clear the DR bit so that we operate on physical
> 	 * rather than virtual addresses
> 	 */
> 	msr = mfmsr();
> 	mtmsr(msr & ~(MSR_DR));
> 
> 	/* Write out the data cache */
> 	for (i = 0; i < dlines; i++, address += dbytes)
> 		dcbst((void *)address);
> 
> 	/* Invalidate the instruction cache */
> 	address = addr;
> 	for (i = 0; i < ilines; i++, address += ibytes)
> 		icbi((void *)address);
> 
> 	mtmsr(msr);
> }
> 
> void test_flush_phys(unsigned long addr)
> {
> 	flush_dcache_icache_phys(addr);
> }
> 
> 
> This gives the following assembler (using pmac32_defconfig):
> 000003cc <test_flush_phys>:
>   3cc:   94 21 ff f0     stwu    r1,-16(r1)
>   3d0:   7d 00 00 a6     mfmsr   r8
>   3d4:   55 09 07 34     rlwinm  r9,r8,0,28,26
>   3d8:   7d 20 01 24     mtmsr   r9
>   3dc:   39 20 00 80     li      r9,128
>   3e0:   7d 29 03 a6     mtctr   r9
>   3e4:   39 43 10 00     addi    r10,r3,4096
>   3e8:   7c 69 1b 78     mr      r9,r3
>   3ec:   7c 00 48 6c     dcbst   0,r9
>   3f0:   39 29 00 20     addi    r9,r9,32
>   3f4:   42 00 ff f8     bdnz    3ec <test_flush_phys+0x20>
>   3f8:   7c 00 1f ac     icbi    0,r3
>   3fc:   38 63 00 20     addi    r3,r3,32
>   400:   7f 8a 18 40     cmplw   cr7,r10,r3
>   404:   40 9e ff f4     bne     cr7,3f8 <test_flush_phys+0x2c>
>   408:   7d 00 01 24     mtmsr   r8
>   40c:   38 21 00 10     addi    r1,r1,16
>   410:   4e 80 00 20     blr
> 
>