On Fri, Jul 26, 2019 at 12:36 AM Philipp Zabel p.zabel@pengutronix.de wrote:
On Thu, 2019-07-25 at 11:17 -0300, Ezequiel Garcia wrote:
From: Francois Buergisser fbuergisser@chromium.org
The Hantro codec is typically used in platforms with an IOMMU, so we need to set a proper DMA segment size.
... to make sure the DMA-mapping subsystem produces contiguous mappings?
Devices without an IOMMU will still fallback to default 64KiB segments.
I don't understand this comment. The default max_seg_size may be 64 KiB, but if we are always setting it to DMA_BUT_MASK(32), there is no falling back.
DMA mask and segment size are two completely orthogonal parameters. Please check https://elixir.bootlin.com/linux/v5.3-rc1/source/drivers/iommu/dma-iommu.c#L... for an example of how the latter is used.
Best regards, Tomasz