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Date:   Mon, 10 Aug 2020 02:01:46 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "Michael Ellerman" <mpe@...erman.id.au>
CC:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hamish Martin <Hamish.Martin@...iedtelesis.co.nz>
Subject: Re: [PATCH] powerpc/legacy_serial: Use early_ioremap()


On 24/03/20 10:54 am, Chris Packham wrote:
> Hi Christophe,
>
> On Wed, 2020-02-05 at 12:03 +0000, Christophe Leroy wrote:
>> [    0.000000] ioremap() called early from
>> find_legacy_serial_ports+0x3cc/0x474. Use early_ioremap() instead
>>
> I was just about to dig into this error message and found you patch. I
> applied it to a v5.5 base.
>
>> find_legacy_serial_ports() is called early from setup_arch(), before
>> paging_init(). vmalloc is not available yet, ioremap shouldn't be
>> used that early.
>>
>> Use early_ioremap() and switch to a regular ioremap() later.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> On my system (Freescale T2080 SOC) this seems to cause a crash/hang in
> early boot. Unfortunately because this is affecting the boot console I
> don't get any earlyprintk output.

I've been doing a bit more digging into why Christophe's patch didn't 
work for me. I noticed the powerpc specific early_ioremap_range() 
returns addresses around ioremap_bot. Yet the generic early_ioremap() 
uses addresses around FIXADDR_TOP. If I try the following hack I can 
make Christophe's patch work

diff --git a/arch/powerpc/include/asm/fixmap.h 
b/arch/powerpc/include/asm/fixmap.h
index 2ef155a3c821..7bc2f3f73c8b 100644
--- a/arch/powerpc/include/asm/fixmap.h
+++ b/arch/powerpc/include/asm/fixmap.h
@@ -27,7 +27,7 @@
  #include <asm/kasan.h>
  #define FIXADDR_TOP    (KASAN_SHADOW_START - PAGE_SIZE)
  #else
-#define FIXADDR_TOP    ((unsigned long)(-PAGE_SIZE))
+#define FIXADDR_TOP    (IOREMAP_END - PAGE_SIZE)
  #endif

  /*

I'll admit to being out of my depth. It seems that the generic 
early_ioremap() is not quite correctly plumbed in for powerpc.

>> ---
>>   arch/powerpc/kernel/legacy_serial.c | 33 +++++++++++++++++++++++++
>> ----
>>   1 file changed, 29 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/legacy_serial.c
>> b/arch/powerpc/kernel/legacy_serial.c
>> index f061e06e9f51..8b2c1a8553a0 100644
>> --- a/arch/powerpc/kernel/legacy_serial.c
>> +++ b/arch/powerpc/kernel/legacy_serial.c
>> @@ -15,6 +15,7 @@
>>   #include <asm/udbg.h>
>>   #include <asm/pci-bridge.h>
>>   #include <asm/ppc-pci.h>
>> +#include <asm/early_ioremap.h>
>>   
>>   #undef DEBUG
>>   
>> @@ -34,6 +35,7 @@ static struct legacy_serial_info {
>>   	unsigned int			clock;
>>   	int				irq_check_parent;
>>   	phys_addr_t			taddr;
>> +	void __iomem			*early_addr;
>>   } legacy_serial_infos[MAX_LEGACY_SERIAL_PORTS];
>>   
>>   static const struct of_device_id legacy_serial_parents[] __initconst
>> = {
>> @@ -325,17 +327,16 @@ static void __init
>> setup_legacy_serial_console(int console)
>>   {
>>   	struct legacy_serial_info *info =
>> &legacy_serial_infos[console];
>>   	struct plat_serial8250_port *port =
>> &legacy_serial_ports[console];
>> -	void __iomem *addr;
>>   	unsigned int stride;
>>   
>>   	stride = 1 << port->regshift;
>>   
>>   	/* Check if a translated MMIO address has been found */
>>   	if (info->taddr) {
>> -		addr = ioremap(info->taddr, 0x1000);
>> -		if (addr == NULL)
>> +		info->early_addr = early_ioremap(info->taddr, 0x1000);
>> +		if (info->early_addr == NULL)
>>   			return;
>> -		udbg_uart_init_mmio(addr, stride);
>> +		udbg_uart_init_mmio(info->early_addr, stride);
>>   	} else {
>>   		/* Check if it's PIO and we support untranslated PIO */
>>   		if (port->iotype == UPIO_PORT && isa_io_special)
>> @@ -353,6 +354,30 @@ static void __init
>> setup_legacy_serial_console(int console)
>>   	udbg_uart_setup(info->speed, info->clock);
>>   }
>>   
>> +static int __init ioremap_legacy_serial_console(void)
>> +{
>> +	struct legacy_serial_info *info =
>> &legacy_serial_infos[legacy_serial_console];
>> +	struct plat_serial8250_port *port =
>> &legacy_serial_ports[legacy_serial_console];
>> +	void __iomem *vaddr;
>> +
>> +	if (legacy_serial_console < 0)
>> +		return 0;
>> +
>> +	if (!info->early_addr)
>> +		return 0;
>> +
>> +	vaddr = ioremap(info->taddr, 0x1000);
>> +	if (WARN_ON(!vaddr))
>> +		return -ENOMEM;
>> +
>> +	udbg_uart_init_mmio(vaddr, 1 << port->regshift);
>> +	early_iounmap(info->early_addr, 0x1000);
>> +	info->early_addr = NULL;
>> +
>> +	return 0;
>> +}
>> +early_initcall(ioremap_legacy_serial_console);
>> +
>>   /*
>>    * This is called very early, as part of setup_system() or
>> eventually
>>    * setup_arch(), basically before anything else in this file. This
>> function

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