TR: Linux 2.6.x 82xx probe devices with multiple serial drivers

TR: Linux 2.6.x 82xx probe devices with multiple serial drivers

[Laurent Lagrange]

Hello,

I use a 82xx platform with a device tree which describes 4 SCC ports.
I want to probe these 4 SCC ports against 2 serial drivers (e.g. async and
sync).
Each port is declared as compatible with the 2 drivers.

When the first driver is loaded, all devices are probed and bound
with this driver and cannot be probed against the second driver.

I know that it can be a way to prevent against concurrent accesses but the
configuration is static and depends on how the drivers are loaded.

In fact, I want to load my 2 drivers, probe each entry without requesting
any resource then select how to open my ports using the first or second
driver.

Any tips ?
Thanks
Laurent

Linux 2.6.x: arch powerpc: PCI DMA allocation misunderstandings

[Laurent Lagrange]

Hello,

I use a 82xx or 85xx host platform with a Linux 2.6.24 or 2.2.31.

On this host, I want to write a PCI driver for a target PMC device
wich only supports 30bits (1GB) DMA addressing.
The PMC device is the master of the DMA transfers from/to the host memory.

In the host driver, I begin to set the two DMA masks with 
 - pci_set_dma_mask(pdev, DMA_BIT_MASK(30)) and
 - pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(30))

Then I allocate DMA buffers in the host memory with
 - pci_alloc_consistent or
 - pci_pool_create and pci_pool_alloc

My problem is that the alloc functions return physical addresses
which are coherent with 32bits but not with the wanted 30bits.

The allocations seem to work like a kmalloc with a GFP_DMA flag.
On powerpc architecture, GFP_DMA preserves the allocations on 32bits
unlike on x86 architecture which restrict the allocations on 24bits.

I don't understand why it is recommended to use the PCI DMA API
with the DMA masks if the final allocator is only able to 
use a GFP_DMA-like restriction and not a real provided mask.

Surely I missed something...
Any idea would be welcome.

Thanks
Laurent