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

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Date:	Fri, 24 Sep 2010 13:45:20 -0700
From:	Vernon Mauery <vernux@...ibm.com>
To:	Arnd Bergmann <arnd@...db.de>
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 24-Sep-2010 11:23 AM, Vernon Mauery wrote:
>On 24-Sep-2010 07:40 PM, Arnd Bergmann wrote:
>>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.
>
>No, inb/outb have address as as unsigned long, which would explain 
>why 0x40000 works with PIO.  When doing inb/outb via the 
>ioread/iowrite macros, the port value is the address (minus the 
>offset) masked off to PIO_MASK, which is 16 bits on x86.
>
>So it looks like this really not going to work and I will have to go 
>back to how it was before.  Would it be tacky to write my own little 
>macro?

Okay.  I finally have it.  In one of my changes, I inadvertently changed 
the shape of the struct ibm_rtl_table, which is where I read the ioport 
address from.  This explains why the weird port.  Once I fixed my table 
so it was correct again, the port is 0x600, which is completely 
reasonable and will work just fine with the iowrite functions.  Thanks 
for bringing this up -- it greatly simplifies things.

--Vernon
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