The MSI target address requires to be reserved within the lowest 4GB memory in order to support the PCIe peripherals with no 64-bit MSI TLPs support. Since the allocation is done from the DMA-coherent memory let's modify the allocation procedure to setting the coherent DMA-mask only and avoiding the streaming DMA-mask modification. Thus at least the streaming DMA operations would work with no artificial limitations. It will be specifically useful for the eDMA-capable controllers so the corresponding DMA-engine clients would map the DMA buffers with no need in the SWIOTLB intervention for the buffers allocated above the 4GB memory region. While at it let's add a brief comment about the reason of having the MSI target address allocated from the DMA-coherent memory limited with the 4GB upper bound. Signed-off-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> --- Changelog v8: - This is a new patch added on v8 stage of the series. (@Robin, @Christoph) --- drivers/pci/controller/dwc/pcie-designware-host.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c index 3ab6ae3712c4..e10608af39b4 100644 --- a/drivers/pci/controller/dwc/pcie-designware-host.c +++ b/drivers/pci/controller/dwc/pcie-designware-host.c @@ -366,7 +366,16 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp) dw_chained_msi_isr, pp); } - ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32)); + /* + * Even though the iMSI-RX Module supports 64-bit addresses some + * peripheral PCIe devices may lack the 64-bit messages support. In + * order not to miss MSI TLPs from those devices the MSI target address + * has to be reserved within the lowest 4GB. + * Note until there is a better alternative found the reservation is + * done by allocating from the artificially limited DMA-coherent + * memory. + */ + ret = dma_set_coherent_mask(dev, DMA_BIT_MASK(32)); if (ret) dev_warn(dev, "Failed to set DMA mask to 32-bit. Devices with only 32-bit MSI support may not work properly\n"); -- 2.38.1
