powerpc/nx: Don't pack struct coprocessor_request_block

Building with W=1 results in the following warning:

In file included from arch/powerpc/platforms/powernv/vas-fault.c:16:
./arch/powerpc/include/asm/icswx.h:159:1: error: alignment 1 of ‘struct
	coprocessor_request_block’ is less than 16 [-Werror=packed-not-aligned]
  159 | } __packed;
      | ^
./arch/powerpc/include/asm/icswx.h:159:1: error: alignment 1 of ‘struct
	coprocessor_request_block’ is less than 16 [-Werror=packed-not-aligned]
./arch/powerpc/include/asm/icswx.h:159:1: error: alignment 1 of ‘struct
	coprocessor_request_block’ is less than 16 [-Werror=packed-not-aligned]
./arch/powerpc/include/asm/icswx.h:159:1: error: alignment 1 of ‘struct
	coprocessor_request_block’ is less than 16 [-Werror=packed-not-aligned]
cc1: all warnings being treated as errors

This happens because coprocessor_request_block includes several
sub-structures with an alignment specified using the __aligned(XX)
attribute. The problem comes from coprocessor_request_block having the
__packed attribute. Packing the structure causes the preferred alignment of
the nested structures to be ignored and we get the warnings as a result.

This isn't a problem in practice since the struct is defined with explicit
padding in the form of reserved fields, but we'd like to get rid of the
spurious warnings. The simplest solution is to remove the packed attribute
and use a BUILD_BUG_ON() to ensure the struct is the correct (expected by
HW) size compile time.

Also add a __aligned(128) to the request block structure since Book4 for P8
suggests the HW requires it to be aligned to a 128 byte boundary. There's a
similar requirement for P9 since the COPY and PASTE instructions used to
invoke VAS/NX accelerators operates on a cache line boundary.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200804005410.146094-7-oohall@gmail.com

diff --git a/arch/powerpc/include/asm/icswx.h b/arch/powerpc/include/asm/icswx.h
index b0c70a35fd0edbd96b14ff7e320a1b357ec5d410..f6599ccb3012acfe92e80fa6b3f25a574c6b1caa 100644 (file)
--- a/arch/powerpc/include/asm/icswx.h
+++ b/arch/powerpc/include/asm/icswx.h
@@ -156,8 +156,7 @@ struct coprocessor_request_block {
        u8 reserved[32];
 
        struct coprocessor_status_block csb;
-} __packed;
-
+} __aligned(128);
 
 /* RFC02167 Initiate Coprocessor Instructions document
  * Chapter 8.2.1.1.1 RS
@@ -188,6 +187,9 @@ static inline int icswx(__be32 ccw, struct coprocessor_request_block *crb)
        __be64 ccw_reg = ccw;
        u32 cr;
 
+       /* NB: the same structures are used by VAS-NX */
+       BUILD_BUG_ON(sizeof(*crb) != 128);
+
        __asm__ __volatile__(
        PPC_ICSWX(%1,0,%2) "\n"
        "mfcr %0\n"