On 2023-03-17 18:23, Rob Herring wrote:
+Robin
On Mon, Mar 13, 2023 at 02:40:15PM +0200, Elad Nachman wrote:
From: Elad Nachman <enachman@xxxxxxxxxxx>
Some devices, such as AC5 and AC5X have their physical DDR memory
start at address 0x2_0000_0000. In order to have the DMA coherent
allocation succeed later, a different DMA mask is required, as
defined in the DT file for such SOCs, using dma-ranges.
I'm afraid this is not right. 'dma-ranges' in the PCI host bridge node
applies to PCI devices (i.e. child node), not the host bridge itself.
It's 'dma-ranges' in the parent node of the host bridge that applies
here. The core code will set masks (ranges really now) based on bus
restrictions. The mask for the device should only be based on the
device's limits (i.e. the device is 32-bit only).
I think you will need whatever solution comes out of this thread[1].
Right, "make the allocation succeed later" is entirely missing the point
of this code. The only reason we're doing that allocation at all is to
reserve a 32-bit bus address. If it fails, it means we can't reliably
support endpoints with only a 32-bit MSI capability. Using a bigger mask
in order to successfully reserve a >32-bit bus address basically
*guarantees* that you can't support endpoints with only a 32-bit MSI
capability.
Thanks Rob for digging up that thread; the original idea there should
still be fine, but the alternative suggestion from Serge at the end is
potentially even better for this situation where it's down to the SoC's
memory map rather than the kernel config. It just needs somebody with
sufficient motivation and resources to write and test a patch :)
Robin.
Rob
[1] https://lore.kernel.org/all/c014b074-6d7f-773b-533a-c0500e239ab8@xxxxxxx/
