Hi Kenneth, On Tuesday 18 April 2006 21:19, Kenneth Poole wrote: > Regarding DMA allocation for CPM uarts, we had a similar issue with our > MPC857T and MPC885 boards. I think the real problem is that > bus_to_virt() and virt_to_bus() don't work on 8xx platforms for > addresses allocated using dma_alloc_coherent(). We had a previous > discussion Pantelis Antoniou and he agreed that the use of bus_to_virt() > and virt_to_bus() should be deprecated. This is also recommended in the > whitepaper series that discussed porting device drivers from 2.4 to 2.6.
You are right! I hadn't noticed the (implicit) use of virt_to_bus() in cpm_uart_core.c. In the case that "((unsigned long)addr >= CPM_ADDR)", the address isn't translated, that's why the uart keeps sending lots of 0xff's instead of real data: There is empty flash at that adress (after 0xff100000)! This also explains why the system hangs when I set CONFIG_CONSISTENT_START to 0xfd100000, because then the CPM will access unadressed space. Vitaly: Is it true that your ADS boards both have IMMAP_ADDR < CONFIG_CONSISTENT_START ? That would explain why those do work. On the PQ2's dma_alloc_coherent(), behaves differently, so they might also work. In fact, bus_to_virt(), which is also used, does nothing more than adding KERNELBASE to the address, so a!=bus_to_virt(virt_to_bus(a)) if 'a' is obtained by anything other than kmalloc(). So if 'a' is obtained from dma_alloc_coherent(), will bus_to_virt(virt_to_bus(a)) at least yield a correctly mapped virtual address? I am asking, because line 263 of cpm_uart_core.c does exactly this, and it smells ;-) > What we did was use dma_alloc_coherent() in cpm_uart_cpm1.c, saving > dma_addr in the pinfo structure. The in cpm_uart_core.c, we use dma_addr > as the base address for the cbd_bufaddr values in each of the > descriptors. The software, when accessing the DMA buffers, uses mem_addr > as the base, applying the same offset computed previously for the dma > addresses. This technique is used in other drivers all over 2.6. Sounds like the correct thing to do, but do you (by any chance) have a patch for this change, to share? Thanks a lot to everyone for their comments and help. Greetings, -- David Jander
