Hi Serge,
On Fri, Jun 14, 2019 at 09:33:42AM +0300, Serge Semin wrote:
> There are some generic drivers in the kernel, which make use of the
> q-accessors or their derivatives. While at current asm/io.h the accessors
> are defined, their implementation is only applicable either for 64bit
> systems, or for systems with cpu_has_64bits flag set. Obviously there
> are MIPS systems which are neither of these, but still need to have
> those drivers supported. In this case the solution is to define some
> generic versions of the q-accessors, but with a limitation to be
> non-atomic. Such accessors are defined in the
> io-64-nonatomic-{hi-lo,lo-hi}.h file. The drivers which utilize the
> q-suffixed IO-methods are supposed to include the header file, so
> in case if these accessors aren't defined for the platform, the generic
> non-atomic versions are utilized. Currently the MIPS-specific asm/io.h
> file provides the q-accessors for any MIPS system even for ones, which
> in fact don't support them and raise BUG() in case if any of them is
> called. Due to this the generic versions of the accessors are never
> used while an attempt to call the IO-methods causes the kernel BUG().
> In order to fix this we need to define the q-accessors only for
> the MIPS systems, which actually support them, and don't define them
> otherwise, so to let the corresponding drivers to use the non-atomic
> q-suffixed accessors.
>
> Signed-off-by: Serge Semin <fancer.lan...@gmail.com>
> Suggested-by: Arnd Bergmann <a...@arndb.de>
> Cc: Vadim V. Vlasov <vadim.vla...@t-platforms.ru>
> ---
> arch/mips/include/asm/io.h | 11 +++++++++++
> 1 file changed, 11 insertions(+)
So this seems pretty reasonable. Build testing all our defconfigs only
showed up one issue for decstation_defconfig & decstation_r4k_defconfig:
drivers/net/fddi/defza.c: In function 'fza_reads':
drivers/net/fddi/defza.c:88:17: error: implicit declaration of
function 'readq_relaxed'; did you mean 'readw_relaxed'?
[-Werror=implicit-function-declaration]
#define readq_u readq_relaxed
^~~~~~~~~~~~~
drivers/net/fddi/defza.c:126:13: note: in expansion of macro 'readq_u'
*dst++ = readq_u(src++);
^~~~~~~
drivers/net/fddi/defza.c: In function 'fza_writes':
drivers/net/fddi/defza.c:92:18: error: implicit declaration of
function 'writeq_relaxed'; did you mean 'writel_relaxed'?
[-Werror=implicit-function-declaration]
#define writeq_u writeq_relaxed
^~~~~~~~~~~~~~
drivers/net/fddi/defza.c:151:4: note: in expansion of macro 'writeq_u'
writeq_u(*src++, dst++);
^~~~~~~~
CC net/core/scm.o
cc1: some warnings being treated as errors
make[4]: *** [scripts/Makefile.build:279: drivers/net/fddi/defza.o] Error 1
These uses of readq_relaxed & writeq_relaxed are both conditional upon
sizeof(unsigned long) == 8, ie. upon CONFIG_64BIT=y so they're not going
to present a runtime issue but we need to provide some implementation of
the *q accessors to keep the compiler happy.
I see a few options:
1) We could just have defza.c include <io-64-nonatomic-lo-hi.h> to get
the appropriate declarations, which should then get optimized away by
the compiler anyway & never actually be used.
2) We could have defza.h #define its readq_u & writeq_u macros
differently for CONFIG_32BIT=y kernels, perhaps using
__compiletime_error to catch any bogus use of them.
3) We could do the same in a generic header, though if nobody else has
needed it so far & this is the only place we need it then maybe it's
not worth it.
So I'm thinking option 2 might be best, as below. Having said that I
don't mind option 1 either - it's simple. Maciej do you have any
preference?
Thanks,
Paul
---
diff --git a/drivers/net/fddi/defza.c b/drivers/net/fddi/defza.c
index c5cae8e74dc4..85d6a7f22fe7 100644
--- a/drivers/net/fddi/defza.c
+++ b/drivers/net/fddi/defza.c
@@ -85,11 +85,21 @@ static u8 hw_addr_beacon[8] = { 0x01, 0x80, 0xc2, 0x00,
0x01, 0x00 };
*/
#define readw_u readw_relaxed
#define readl_u readl_relaxed
-#define readq_u readq_relaxed
#define writew_u writew_relaxed
#define writel_u writel_relaxed
-#define writeq_u writeq_relaxed
+
+#ifdef CONFIG_32BIT
+extern u64 defza_readq_u(const void *ptr)
+ __compiletime_error("readq_u should not be used by 32b kernels");
+extern void defza_writeq_u(u64 val, void *ptr)
+ __compiletime_error("writeq_u should not be used by 32b kernels");
+# define readq_u defza_readq_u
+# define writeq_u defza_writeq_u
+#else
+# define readq_u readq_relaxed
+# define writeq_u writeq_relaxed
+#endif
static inline struct sk_buff *fza_alloc_skb_irq(struct net_device *dev,
unsigned int length)
