Hi Arnd,
On 29/4/19 4:44 am, Arnd Bergmann wrote:
On Sun, Apr 28, 2019 at 3:59 PM Greg Ungerer <gerg@xxxxxxxxxxxxxx> wrote:
On 28/4/19 7:21 pm, Arnd Bergmann wrote:
On Sun, Apr 28, 2019 at 10:46 AM Geert Uytterhoeven
<geert@xxxxxxxxxxxxxx> wrote:
On Sat, Apr 27, 2019 at 10:22 PM Angelo Dureghello <angelo@xxxxxxxx> wrote:
On Sat, Apr 27, 2019 at 05:32:22PM +0200, Angelo Dureghello wrote:
Coldfire makes the behavior of readw()/readl() depend on the
MMIO address, presumably since that was the easiest way to
get drivers working originally, but it breaks the assumption
in the asm-generic code.
Yes, that is right.
There is a number of common hardware modules that Freescale have
used in the ColdFire SoC parts and in their ARM based parts (iMX
families). The ARM parts are pretty much always little endian, and
the ColdFire is always big endian. The hardware registers in those
hardware blocks are always accessed in native endian of the processor.
In later Freescale/NXP ARM SoCs (i.MX and Layerscape), we
also get a lot of devices pulled over from PowerPC, with random
endianess. In some cases, the same device that had big-endian
registers originally ends up in two different ARM products and one of
them uses big-endian while the other one uses little-endian registers.
So the address range checks are to deal with those internal
hardware blocks (i2c, spi, dma, etc), since we know those are
at fixed addresses. That leaves the usual endian swapping in place for
other general (ie external) devices (PCI devices, network chips, etc).
Is there a complete list of coldfire on-chip device drivers?
Looking at some of the drivers:
- drivers/i2c/busses/i2c-imx.c uses only 8-bit accesses and works either way,
same for drivers/tty/serial/mcf.c
- drivers/spi/spi-coldfire-qspi.c is apparently coldfire-only and could use
ioread32be for a portable to do big-endian register access.
- edma-common has a wrapper to support both big-endian and little-endian
configurations in the same kernel image, but the mcf interrupt handler
is hardcoded to the (normally) little-endian ioread32 function.
- drivers/net/ethernet/freescale/fec_main.c is shared between coldfire
and i.MX (but not mpc52xx), and is hardcoded to readl/writel, and
would need the same trick as edma to make it portable.
That matches up with what we list out in arch/m68k/coldfire/devices.c.
I can't think of any other drivers.
There is a lot of use readl/writel and friends in the architecture
specific code too, in arch/m68k/coldfire. At first I used __raw_readl/
__raw_writel to always get native endianess. But quote a few uses of
readl/writel have crept in over the years.
Regards
Greg
