device memory mapping

device memory mapping

[Dayton, Dean]

I'm in the process of porting Linux to a proprietary board that has run pSOS
in the past. The board has an MPC860, one ethernet on SCC1, another ethernet
using a Sonic chip, and 4 quad Cirrus Logic CD2401 serial chips.

I started with mpc8xx-2.2.13.tgz. The console and the SCC base ethernet came
up easily. Now I'm trying to port the Sonic driver (which appears to have
been intended for a MIPs machine). Under pSOS, with a flat address space, we
mapped the Sonic base to 0x40000000.

How do I map this address in Linux. Whenever I try to read from the Sonic I
get the following error:

	NIP: C00A7148 XER: 0000FF01 LR: C00A7148 REGS: c048fd90 TRAP: 0300
	MSR: 00009032 EE: 1 PR: 0 FP: 0 ME: 1 IR/DR: 11
	TASK = c048e000[1] 'swapper' mm->pgd c00c7000 Last syscall: 120 last
math 00000000
	GPR00: C00A7148 C048FE40 C048E000 00000019 00000001 00000019
00000001 C0490720
	GPR08: FF002830 C00E0000 00000019 C048FD80 88400022 00012FF0
0009C101 C1062840
	GPR16: C3A67D1B 00101800 C3A67D1B 00100000 00900000 001001C4
00210000 00002C78
	GPR24: 00000000 00E00000 00000001 0020000D 40000000 C00D6510
40000000 C00D6890
	Call backtrace:
	C00A7148 C00A70EC C00A6C64 C00A6D38 C00631A4 C00988CC C00032EC
	C0003408 C000783C 7C0802A6
	Kernel panic: kernel access of bad area pc c00a7148 lr c00a7148
address 400000A0 tsk swapper/1

I suspect I need to tell the MMU about the Sonic. But I don't know how. I'm
also a little confused about whether I need to worry about physical/virtual
address mapping. Any help would be appreciated.

Thanks
 Dean Dayton - dean@aiinet.com

PS: Are there any good HOWTO/guides to writing device drivers on a LinuxPPC
port?

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Re: device memory mapping

[Dan Malek]

"Dayton, Dean" wrote:

> How do I map this address in Linux.

Very carefully....seriously.  You will need to do ioremap() of the
address, and it will return a virtual address to you.  The very
carefully part comes from you having to do this after the kernel
virtual memory allocator has been initialized.  Don't do this ioremap()
in the mm/init.c function, but rather in the device driver initialization
(or open, or whatever seems appropriate).  It should return a virtual
address something like 0xc4xxxxxx.  Then, have at it!


	-- Dan

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Re: device memory mapping

[Graham Stoney]

Dayton, Dean writes:
> PS: Are there any good HOWTO/guides to writing device drivers on a LinuxPPC
> port?

Most of it is probably architecture-independent, which is a good goal for new
drivers anyway, so stuff like the Linux Kernel Module Programming Guide might
help, at:
    http://metalab.unc.edu/mdw/LDP/lkmpg/mpg.html

There are also some 8xx-specific driver examples that might be helpful listed
in the HOWTO at:
    http://members.xoom.com/greyhams/linux/PowerPC-Embedded-HOWTO-11.html

Regards,
Graham

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