cgem: improve usage of busdma(9) KPI

BUS_DMA_NOCACHE should only be used when one needs to guarantee the
created mapping has uncached memory attributes, usually as a result
of buggy hardware. Normal use cases should pass BUS_DMA_COHERENT, to
create an appropriate mapping based on the flags passed to
bus_dma_tag_create().

This should have no functional change, since the DMA tags in this driver
are created without the BUS_DMA_COHERENT flag.

Reported by:	mmel
Reviewed by:	mmel, Thomas Skibo <thomas-bsd@skibo.net>
MFC after:	3 days

1 files changed, 4 insertions, 8 deletions

diff --git a/sys/dev/cadence/if_cgem.c b/sys/dev/cadence/if_cgem.c
index 81fc39b831af..0583e846458a 100644
--- a/sys/dev/cadence/if_cgem.c
+++ b/sys/dev/cadence/if_cgem.c
@@ -443,17 +443,13 @@ cgem_setup_descs(struct cgem_softc *sc)
 		return (err);
 
 	/*
-	 * Allocate DMA memory in non-cacheable space.  We allocate transmit,
-	 * receive and null descriptor queues all at once because the
-	 * hardware only provides one register for the upper 32 bits of
-	 * rx and tx descriptor queues hardware addresses.
+	 * Allocate DMA memory. We allocate transmit, receive and null
+	 * descriptor queues all at once because the hardware only provides
+	 * one register for the upper 32 bits of rx and tx descriptor queues
+	 * hardware addresses.
 	 */
 	err = bus_dmamem_alloc(sc->desc_dma_tag, (void **)&sc->rxring,
-#ifdef __arm__
 	    BUS_DMA_NOWAIT | BUS_DMA_COHERENT | BUS_DMA_ZERO,
-#else
-	    BUS_DMA_NOWAIT | BUS_DMA_NOCACHE | BUS_DMA_ZERO,
-#endif
 	    &sc->rxring_dma_map);
 	if (err)
 		return (err);