Re: [RFC PATCH] powerpc: Convert ____flush_dcache_icache_phys() to C

[Christophe Leroy]

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