Re: [PATCH 3/7] soc: fsl: qe: avoid ppc-specific io accessors

On 22/10/2019 17.01, Christophe Leroy wrote:

On 10/18/2019 12:52 PM, Rasmus Villemoes wrote:

quoted

In preparation for allowing to build QE support for architectures
other than PPC, replace the ppc-specific io accessors. Done via

This patch is not transparent in terms of performance, functions get
changed significantly.

Before the patch:

00000330 <ucc_fast_enable>:
 330:    81 43 00 04     lwz     r10,4(r3)
 334:    7c 00 04 ac     hwsync
 338:    81 2a 00 00     lwz     r9,0(r10)
 33c:    0c 09 00 00     twi     0,r9,0
 340:    4c 00 01 2c     isync
 344:    70 88 00 02     andi.   r8,r4,2
 348:    41 82 00 10     beq     358 <ucc_fast_enable+0x28>
 34c:    39 00 00 01     li      r8,1
 350:    91 03 00 10     stw     r8,16(r3)
 354:    61 29 00 10     ori     r9,r9,16
 358:    70 88 00 01     andi.   r8,r4,1
 35c:    41 82 00 10     beq     36c <ucc_fast_enable+0x3c>
 360:    39 00 00 01     li      r8,1
 364:    91 03 00 14     stw     r8,20(r3)
 368:    61 29 00 20     ori     r9,r9,32
 36c:    7c 00 04 ac     hwsync
 370:    91 2a 00 00     stw     r9,0(r10)
 374:    4e 80 00 20     blr

After the patch:

0000030c <ucc_fast_enable>:
 30c:    94 21 ff e0     stwu    r1,-32(r1)
 310:    7c 08 02 a6     mflr    r0
 314:    bf a1 00 14     stmw    r29,20(r1)
 318:    7c 9f 23 78     mr      r31,r4
 31c:    90 01 00 24     stw     r0,36(r1)
 320:    7c 7e 1b 78     mr      r30,r3
 324:    83 a3 00 04     lwz     r29,4(r3)
 328:    7f a3 eb 78     mr      r3,r29
 32c:    48 00 00 01     bl      32c <ucc_fast_enable+0x20>
            32c: R_PPC_REL24    ioread32be
 330:    73 e9 00 02     andi.   r9,r31,2
 334:    41 82 00 10     beq     344 <ucc_fast_enable+0x38>
 338:    39 20 00 01     li      r9,1
 33c:    91 3e 00 10     stw     r9,16(r30)
 340:    60 63 00 10     ori     r3,r3,16
 344:    73 e9 00 01     andi.   r9,r31,1
 348:    41 82 00 10     beq     358 <ucc_fast_enable+0x4c>
 34c:    39 20 00 01     li      r9,1
 350:    91 3e 00 14     stw     r9,20(r30)
 354:    60 63 00 20     ori     r3,r3,32
 358:    80 01 00 24     lwz     r0,36(r1)
 35c:    7f a4 eb 78     mr      r4,r29
 360:    bb a1 00 14     lmw     r29,20(r1)
 364:    7c 08 03 a6     mtlr    r0
 368:    38 21 00 20     addi    r1,r1,32
 36c:    48 00 00 00     b       36c <ucc_fast_enable+0x60>
            36c: R_PPC_REL24    iowrite32be

True. Do you know why powerpc uses out-of-line versions of these
accessors when !PPC_INDIRECT_PIO, i.e. at least all of PPC32? It's quite
a bit beyond the scope of this series, but I'd expect moving most if not
all of arch/powerpc/kernel/iomap.c into asm/io.h (guarded by
!defined(CONFIG_PPC_INDIRECT_PIO) of course) as static inlines would
benefit all ppc32 users of iowrite32 and friends.

Is there some other primitive available that (a) is defined on all
architectures (or at least both ppc and arm) and (b) expands to good
code in both/all cases?

Note that a few uses of the the iowrite32be accessors has already
appeared in the qe code with the introduction of the qe_clrsetbits()
helpers in bb8b2062af.

Rasmus