[PATCH 2/2] [RFC] nvme-pci: Respect bus DMA constraints

[marek.vasut@gmail.com]

From: Marek Vasut <marek.vasut+renesas@gmail.com>

Since commit 6c2fb2ea7636 ("of/device: Set bus DMA mask as appropriate"),
the upstream bus can constraint device DMA range. Respect that constraint
and do not change the device DMA masks if they were already set.

This is applicable e.g. on systems where the PCIe controller cannot expose
the full address space range. Such a system may have a 64bit CPU with DRAM
mapped both below and above the 32bit address space, yet the PCIe devices
can not perform DMA directly to/from the DRAM range above the 32bit limit.
Hence, for such setup to work, all the buffers must exist below the 32bit
limit.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Jens Axboe <axboe@fb.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: linux-renesas-soc@vger.kernel.org
To: linux-ide@vger.kernel.org
To: linux-nvme@lists.infradead.org
---
 drivers/nvme/host/pci.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 92bad1c810ac..8ec873fb86b1 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2323,7 +2323,8 @@ static int nvme_pci_enable(struct nvme_dev *dev)
 
 	pci_set_master(pdev);
 
-	if (dma_set_mask_and_coherent(dev->dev, DMA_BIT_MASK(64)) &&
+	if (!dev->dev->coherent_dma_mask &&
+	    dma_set_mask_and_coherent(dev->dev, DMA_BIT_MASK(64)) &&
 	    dma_set_mask_and_coherent(dev->dev, DMA_BIT_MASK(32)))
 		goto disable;
 
-- 
2.20.1