在2025年1月13日一月 下午10:16，Mateusz Jończyk写道：
> Hello,
>
> On Linux 6.13-rc6 for mipsel in QEMU on the Malta platform, the RTC CMOS
> driver does not load and /sys/class/rtc is empty. I have tested this with
> "make malta_defconfig", which compiles this driver into the kernel
> (CONFIG_RTC_DRV_CMOS=y).
Hi Mateusz,
Thanks for tracking it down, this is indeed a huge effort.
>
> I have bisected this down to:
>
> commit 4bfb53e7d317c01f296b2feb2fae7c421c1d52dc
> Author: Jiaxun Yang<jiaxun.yang@xxxxxxxxxxx>
> Date: Thu Sep 21 19:04:22 2023 +0800
>
> mips: add <asm-generic/io.h> including
> With the adding, some default ioremap_xx methods defined in
> asm-generic/io.h can be used. E.g the default ioremap_uc() returning
> NULL.
> We also massaged various headers to avoid nested includes.
#regzbot introduced: 4bfb53e7d317c01f296b2feb2fae7c421c1d52dc
>
> I have tried to debug this.
>
> The fallout is apparently limited to the CMOS RTC driver, other
> drivers that access IO ports seem to function correctly (e.g. the
> PATA driver). Also, the read_persistent_clock64 function in
> arch/mips/mti-malta/malta-time.c, which accesses the same hardware
> works correctly.
>
> The CMOS RTC driver is likely special because this device is defined
> in a devicetree (arch/mips/boot/dts/mti/malta.dts) and there it is
> the only defined device on the ISA bus.
>
> That driver fails to load because the call to
>
> platform_get_resource(pdev, IORESOURCE_IO, 0);
>
> in cmos_platform_probe in drivers/rtc/rtc-cmos.c returns NULL.
>
> The mediator seems to be that this bad commit causes
> arch/mips/include/asm/io.h
> to #include <asm-generic/io.h> at the end. As a side effect, this causes
> the PCI_IOBASE macro to be defined:
>
> #ifndef PCI_IOBASE
> #define PCI_IOBASE ((void __iomem *)0)
> #endif
>
> That PCI_IOBASE value above is AFAIK incorrect for MIPS (it should be
> defined to mips_io_port_base as far as I can tell), but this does not
> matter much here.
You are right, this is what should be done.
A quick fix would be #undef PCI_IOBASE in arch/mips/include/asm/io.h
just after including #include <asm-generic/io.h>, with ralink and loongson64
as exception.
In the long term, we should scrutinize platform usage of mips_io_base
following ralink's approach.
>
> When that macro is defined, pci_address_to_pio() in pci.c calls the
> logic_pio_trans_cpuaddr() function, which fails. Removing that ifdef
> in this function "fixes" the issue and allows that driver to load and work
> apparently correctly:
>
> ----------8<------------------
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 661f98c6c63a..368cd9ca6801 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4213,14 +4213,10 @@ EXPORT_SYMBOL_GPL(pci_pio_to_address);
> unsigned long __weak pci_address_to_pio(phys_addr_t address)
> {
> -#ifdef PCI_IOBASE
> - return logic_pio_trans_cpuaddr(address);
> -#else
> if (address > IO_SPACE_LIMIT)
> return (unsigned long)-1;
> return (unsigned long) address;
> -#endif
> }
> /**
> ----------8<------------------
>
> Additionally, the following message appears in dmesg on affected kernels:
>
> LOGIC PIO: addr 0x00000070 not registered in io_range_list
>
> (0x0070 is the IO port address of the CMOS RTC).
>
> When I added dump_stack() in logic_pio_trans_cpuaddr(), which prints
> this warning,
> I got the following:
>
> ----------8<------------------
> Call Trace:
> [<801185c8>] show_stack+0x38/0x118
> [<8010be24>] dump_stack_lvl+0x7c/0xbc
> [<80841060>] logic_pio_trans_cpuaddr+0x88/0x98
> [<80604bec>] __of_address_to_resource+0x208/0x228
> [<805ff45c>] of_device_alloc+0x7c/0x1ac
> [<805ff778>] of_platform_device_create_pdata+0x60/0xf8
> [<805ff9cc>] of_platform_bus_create+0x1b0/0x238
> [<805ffa14>] of_platform_bus_create+0x1f8/0x238
> [<805ffbd8>] of_platform_populate+0x80/0xf8
> [<80a60008>] of_platform_default_populate_init+0xcc/0xe4
> [<8011010c>] do_one_initcall+0x50/0x2b4
> [<80a3d0f0>] kernel_init_freeable+0x1f8/0x2a0
> [<8086975c>] kernel_init+0x24/0x118
> [<801124f8>] ret_from_kernel_thread+0x14/0x1c
> ----------8<------------------
>
> It appears that some call to logic_pio_register_range() from
> lib/logic_pio.c is missing.
> Perhaps the reserve_pio_range() function in arch/mips/loongson64/init.c
> could
> be reused, but that's too deep water for me.
Sadly that is not going to work as those MIPS platforms are not using
vmmap for PCI IO access :-(
>
> Steps to reproduce:
>
> ----------8<------------------
>
> wget
> https://ftp.debian.org/debian/dists/Debian12.9/main/installer-mipsel/current/images/malta/netboot/initrd.gz
>
> CROSS_COMPILE=mipsel-linux-gnu- ARCH=mips make malta_defconfig
>
> CROSS_COMPILE=mipsel-linux-gnu- ARCH=mips make -j4
>
> qemu-system-mipsel -machine malta -cpu 24Kf -m 1g -nographic -kernel
> vmlinuz \
> -initrd initrd.gz \
> -append "console=ttyS0 debug ignore_loglevel"
>
> ----------8<------------------
>
>
> Greetings,
>
> Mateusz
--
- Jiaxun
