Re: [PATCH 6/6] m68k/nommu: stop using GENERIC_IOMAP

From: Greg Ungerer
Date: Mon Mar 24 2025 - 09:51:37 EST

Hi Arnd,

On 24/3/25 18:02, Arnd Bergmann wrote:
On Mon, Mar 24, 2025, at 02:33, Greg Ungerer wrote:
Hi Arnd,

On 15/3/25 20:59, Arnd Bergmann wrote:
From: Arnd Bergmann <arnd@xxxxxxxx>

There is no need to go through the GENERIC_IOMAP wrapper for PIO on
nommu platforms, since these always come from PCI I/O space that is
itself memory mapped.

Instead, the generic ioport_map() can just return the MMIO location
of the ports directly by applying the PCI_IO_PA offset, while
ioread32/iowrite32 trivially turn into readl/writel as they do
on most other architectures.

Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

With this applied this fails to build for me:

UPD include/generated/utsversion.h
CC init/version-timestamp.o
LD vmlinux
m68k-linux-uclibc-ld: drivers/pci/quirks.o: in function
`quirk_switchtec_ntb_dma_alias':
quirks.c:(.text+0x23e4): undefined reference to `pci_iomap'
m68k-linux-uclibc-ld: quirks.c:(.text+0x24fe): undefined reference to
`pci_iounmap'
m68k-linux-uclibc-ld: drivers/pci/quirks.o: in function
`disable_igfx_irq':
quirks.c:(.text+0x32f4): undefined reference to `pci_iomap'
m68k-linux-uclibc-ld: quirks.c:(.text+0x3348): undefined reference to
`pci_iounmap'

Thanks for the report, I was able to reproduce the problem now
and applied the fixup below. I had tested m5475evb_defconfig earlier,
and that built cleanly with PCI enabled, but I had missed how
that still used GENERIC_IOMAP because it has CONFIG_MMU enabled.

Does this fixup work for you?

Yes, this looks good, works for me.
Feel free to add this if you like:

Acked-by: Greg Ungerer <gerg@xxxxxxxxxxxxxx>


On a related note, I'm curious about how the MCF54xx chips are
used in practice, as I see that they are the only coldfire chips
with PCI and they all have an MMU. Are there actual users of these
chips that have PCI but choose not to use the MMU?

No, I think everyone with these uses them with MMU enabled.

It is probably more of an historical curiosity to use them with
the MMU disabled. That supported pre-dated mainline kernels having
full ColdFire MMU support by a good few years.

Regards
Greg



Arnd

8<-----
From a36995e2a64711556c6773797367d165828f6705 Mon Sep 17 00:00:00 2001
From: Arnd Bergmann <arnd@xxxxxxxx>
Date: Mon, 24 Mar 2025 07:53:47 +0100
Subject: [PATCH] m68k: coldfire: select PCI_IOMAP for PCI

After I dropped CONFIG_GENERIC_IOMAP, some PCI drivers started failing
to link when CONFIG_MMU is disabled:

ERROR: modpost: "pci_iounmap" [drivers/video/fbdev/i740fb.ko] undefined!
ERROR: modpost: "pci_iounmap" [drivers/video/fbdev/vt8623fb.ko] undefined!
ERROR: modpost: "pci_iomap_wc" [drivers/video/fbdev/vt8623fb.ko] undefined!
ERROR: modpost: "pci_iomap" [drivers/video/fbdev/vt8623fb.ko] undefined!
ERROR: modpost: "pci_iounmap" [drivers/video/fbdev/s3fb.ko] undefined!
...

It turns out that there were two mistakes in my patch: on !MMU I forgot
to enable CONFIG_GENERIC_PCI_IOMAP, and for Coldfire with MMU enabled,
teh GENERIC_IOMAP was left in place but incorrectly configured.

Fixes: 9d48cc07d0d7 ("m68k/nommu: stop using GENERIC_IOMAP")
Reported-by: Greg Ungerer <gerg@xxxxxxxxxxxxxx>
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index b50c275fa94d..eb5bb6d36899 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -18,12 +18,13 @@ config M68K
select DMA_DIRECT_REMAP if M68K_NONCOHERENT_DMA && !COLDFIRE
select GENERIC_ATOMIC64
select GENERIC_CPU_DEVICES
- select GENERIC_IOMAP if HAS_IOPORT && MMU
+ select GENERIC_IOMAP if HAS_IOPORT && MMU && !COLDFIRE
select GENERIC_IRQ_SHOW
select GENERIC_LIB_ASHLDI3
select GENERIC_LIB_ASHRDI3
select GENERIC_LIB_LSHRDI3
select GENERIC_LIB_MULDI3
+ select GENERIC_PCI_IOMAP if PCI
select HAS_IOPORT if PCI || ISA || ATARI_ROM_ISA
select HAVE_ARCH_LIBGCC_H
select HAVE_ARCH_SECCOMP