Re: [BUG?] crypto: caam: little/big endianness on ARM vs PPC

[Russell King - ARM Linux]

On Mon, Jun 15, 2015 at 06:33:17PM +0200, Jon Nettleton wrote:
> Funny enough I tackled this problem over the weekend as well.  My
> approach was to switch the driver over to use the *_relaxed() io
> functions and then special case the bits missing from the various
> ARCHs.  Basically adding setbits32 and clrbits32 for !PPC
> architectures and letting PPC and ARM share a writeq/readq set of
> functions.  I left the existing LITTLE_ENDIAN special case until I
> could verify if it was needed, or had been tested.

I'll follow up here with what I've mentioned elsewhere, and some further
thoughts.

I think this shows the dangers of using struct { } to define register
offsets.  Let's start here:

/*
 * caam_job_ring - direct job ring setup
 * 1-4 possible per instantiation, base + 1000/2000/3000/4000
 * Padded out to 0x1000
 */
struct caam_job_ring {
        /* Input ring */
        u64 inpring_base;       /* IRBAx -  Input desc ring baseaddr */
        u32 rsvd1;

Apparently, this is a CPU-endian 64-bit value (it's not defined using
le64 or be64 which would "fix" it's endian.)

The second question, which comes up in light of the breakage that's
being reported is: is this really a 64-bit register, or is it a pair
of 32-bit registers side-by-side?

The documentation I'm looking at doesn't document the register at
base + 0x1000, but documents the one at base + 0x1004, and the one
at 0x1004 is given the name "IRBAR0_LS", which presumably stands
for "input ring base address register 0, least significant".

As the code originally stood for PPC, IRBAR0_LS is also at 0x1004,
but appears to be big endian.

On ARM, IRBAR0_LS appears at the same address, but is little endian.

This is *not* a 64-bit register at all, but is a pair of 32-bit
registers side by side.  Moreover, readq() should not be used - no
amount of arch mangling could ever produce a sane readq() which
coped with this.

So, the CAAM code is buggy in this regard: using readq() here when
endian-portability is required is wrong.  It's got to be two 32-bit
reads or two 32-bit writes in the appropriate endian.

Also, note that there's a big difference between __raw_readl() and
readl_relaxed().  readl_relaxed() is always little-endian.  __raw_readl()
is god-knows-what-the-archtecture-decides endian.  Switching PPC
drivers from __raw_readl() to readl_relaxed() is really not a good
idea unless someone from the PPC camp reviews and tests the code.

So, what I'd suggest is just fixing rd_reg64() and wr_reg64() to do
the right thing: keeping the two 32-bit words in the same order
irrespective of the endian-ness, and staying with the __raw_*
accessors until PPC people can look at this.

-- 
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/