linux-kernel - Re: [RFC][Patch] IBM Real-Time "SMI Free" mode driver -v4

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Date:	Fri, 24 Sep 2010 19:40:18 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Vernon Mauery <vernux@...ibm.com>
Cc:	Randy Dunlap <rdunlap@...otime.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Keith Mannthey <kmannth@...ibm.com>
Subject: Re: [RFC][Patch] IBM Real-Time "SMI Free" mode driver -v4

On Friday 24 September 2010 19:09:43 Vernon Mauery wrote:
> I looked into this and tested it on some hardware, but it doesn't work.  
> After more digging and poking, it looks like the reason is that the port 
> IO address is not within the x86 standard port IO range.
> 
> I tried something like this:
> 
>                         addr = ioread32(&rtl_table->cmd_port_address);
>                         plen = rtl_cmd_width/8;
>                         if (rtl_cmd_type == RTL_ADDR_TYPE_MMIO)
>                                 rtl_cmd_addr = ioremap(addr, plen);
>                         else
>                                 rtl_cmd_addr = ioport_map(addr, plen);
>                         RTL_DEBUG("rtl_cmd_addr = %#llx\n", (u64)rtl_cmd_addr);
> 
> It printed out that rtl_cmd_addr was 0, meaning the ioport_map failed.  
> After more digging, it turns out that on at least one of the machines 
> this code is targeted for, the port IO address (from the first line 
> above) is 0x40000.  Even if this did get mapped, the IO_COND macro would 
> target it for MMIO access instead of PIO access.  So I don't think I can 
> use this method (even though it did make my code a lot nicer to read).
> 
> Any suggestions?

That seems really strange. I thought the inb/outb instructions could not
actually operate on addresses above 0x10000 at all, since they take a 16
bit address operand (DX register). Passing 0x40000 into inb should have the
same effect as zero AFAICT, which means that your existing code should not
work either.

For non-x86 architectures, I would recommend defining HAVE_ARCH_PIO_SIZE
and setting PIO_RESERVED to a higher value.

	Arnd
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