Re: [PATCH4/4] [POWERPC] Fix cpm_uart driver

From: Jochen Friedrich
Date: Tue Sep 25 2007 - 08:09:42 EST

Hi Scott,
Yikes. Please don't change cpm_uart_cpm1.h, as it's correct for arch/powerpc, and there are numerous other places that assume cpmp is virtual (including in the very same function that assigns it a physical address).

I'm still not convinced cpm_uart_cpm1.h is correct:

pinfo->rx_bd_base and pinfo->tx_bd_base are both initialized with an address obtained by cpm_dpram_addr(). In both ppc and powerpc, this is an address relative to dpram_vbase in commproc.c

In cpm_uart_core.c, the operation "pinfo->rx_bd_base - DPRAM_BASE" is used to calculate the DPRAM offset. So DPRAM_BASE must be relative to dpram_vbase in commproc.c as well. However, cpm_uart_cpm1.h uses cpmp in commproc.c to initialize DPRAM_BASE.

On ARCH=ppc, cpmp is a physical address with 1:1 virtual mapping ("well known address"). On ARC=powerpc, this is an address obtained by ioremap(), however it's a different ioremap() call than dpram_vbase is obtained from, so noone can guarantee
cpmp is always the same as dpram_vbase even on ARCH=powerpc.

To me, it looks like setting DPRAM_BASE to cpm_dpram_addr(0) is the fix as it makes the DPRAM offset a defined result.


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