Message-ID: <90b5b76d-25b6-4cdc-91ed-07ac930dc519@o2.pl>
Date: Mon, 13 Jan 2025 23:16:37 +0100
From: Mateusz Jończyk <mat.jonczyk@...pl>
To: linux-mips@...r.kernel.org, linux-arch@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Baoquan He <bhe@...hat.com>, Jiaxun Yang <jiaxun.yang@...goat.com>,
 Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
 Arnd Bergmann <arnd@...db.de>,
 Alexandre Belloni <alexandre.belloni@...tlin.com>,
 regressions@...ts.linux.dev
Subject: [REGRESSION] mipsel: no RTC CMOS on the Malta platform in QEMU

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).

I have bisected this down to:

commit 4bfb53e7d317c01f296b2feb2fae7c421c1d52dc
Author: Jiaxun Yang<jiaxun.yang@...goat.com>
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.

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.

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.

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

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