linux-kernel - Re: endianness swapped

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Message-ID: <CAMuHMdXNCxHP=BWPOy70LjNJoMH+zy7yYOHj29gYt79_5=4ffg@mail.gmail.com>
Date:   Sun, 28 Apr 2019 10:46:03 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Angelo Dureghello <angelo@...am.it>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Linux/m68k" <linux-m68k@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: endianness swapped

Hi Angelo,

CC commit relations

On Sat, Apr 27, 2019 at 10:22 PM Angelo Dureghello <angelo@...am.it> wrote:
> On Sat, Apr 27, 2019 at 05:32:22PM +0200, Angelo Dureghello wrote:
> > as you may know, i am working on mcf5441x.
> > Sorry for not following carefully all the threads, but from a certain
> > kernel version (likely 4.19 or near there), seems ioread32be
> > reads the bytes swapped in endianness (mcf-edma dma driver not working
> > anymore).
> >
> > Has there been a change about this in the architecture I/O access ?
> > How should i proceed now ? Fixing the DMA driver read/write, or what ?

> looks like the reason of my ioread32be now swapped is:
>
> https://patchwork.kernel.org/patch/10766673/
>
> Trying to figure out what to do now.

This is commit aecc787c06f4300f ("iomap: Use non-raw io functions for
io{read|write}XXbe"):

--- a/lib/iomap.c
+++ b/lib/iomap.c
@@ -65,8 +65,8 @@ static void bad_io_access(unsigned long port, const
char *access)
 #endif

 #ifndef mmio_read16be
-#define mmio_read16be(addr) be16_to_cpu(__raw_readw(addr))
-#define mmio_read32be(addr) be32_to_cpu(__raw_readl(addr))
+#define mmio_read16be(addr) swab16(readw(addr))
+#define mmio_read32be(addr) swab32(readl(addr))
 #endif

 unsigned int ioread8(void __iomem *addr)
@@ -106,8 +106,8 @@ EXPORT_SYMBOL(ioread32be);
 #endif

 #ifndef mmio_write16be
-#define mmio_write16be(val,port) __raw_writew(be16_to_cpu(val),port)
-#define mmio_write32be(val,port) __raw_writel(be32_to_cpu(val),port)
+#define mmio_write16be(val,port) writew(swab16(val),port)
+#define mmio_write32be(val,port) writel(swab32(val),port)

On big endian, the raw accessors are assumed to be non-swapping,
while non-raw accessors are assumed to be swapping.
The latter is not true for Coldfire internal registers, cfr.
arch/m68k/include/asm/io_no.h:

static inline u16 readw(const volatile void __iomem *addr)
{
        if (cf_internalio(addr))
                return __raw_readw(addr);
        return __le16_to_cpu(__raw_readw(addr));
}

Orthogonal to how Coldfire's read[wl]() should be fixed, I find it a bit
questionable to swap data twice on big endian architectures.

Fortunately we can avoid that by defining our own
mmio_{read,write}{16,32}be()...

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds