dmaengine: at_hdmac: Don't allow CPU to reorder channel enable

commit 580ee84405c27d6ed419abe4d2b3de1968abdafd upstream.

at_hdmac uses __raw_writel for register writes. In the absence of a
barrier, the CPU may reorder the register operations.
Introduce a write memory barrier so that the CPU does not reorder the
channel enable, thus the start of the transfer, without making sure that
all the pre-required register fields are already written.

Fixes: dc78baa2b90b ("dmaengine: at_hdmac: new driver for the Atmel AHB DMA Controller")
Reported-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/lkml/13c6c9a2-6db5-c3bf-349b-4c127ad3496a@axentia.se/
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20221025090306.297886-1-tudor.ambarus@microchip.com
Link: https://lore.kernel.org/r/20221025090306.297886-14-tudor.ambarus@microchip.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
index 88e8d692f3366a03e8ef48cf9f9dd96130c96c98..526efb8b283b794fbfe6a5ed87ed20e54edb9645 100644 (file)
--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -253,6 +253,8 @@ static void atc_dostart(struct at_dma_chan *atchan, struct at_desc *first)
                       ATC_SPIP_BOUNDARY(first->boundary));
        channel_writel(atchan, DPIP, ATC_DPIP_HOLE(first->dst_hole) |
                       ATC_DPIP_BOUNDARY(first->boundary));
+       /* Don't allow CPU to reorder channel enable. */
+       wmb();
        dma_writel(atdma, CHER, atchan->mask);
 
        vdbg_dump_regs(atchan);