ARM: PL011: add DMA burst threshold support for ST variants
ST Micro variants has some specific dma burst threshold compensation,
which allows them to make better use of a DMA controller. Add support
to set this up.
Based on a patch from Linus Walleij.
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/drivers/serial/amba-pl011.c b/drivers/serial/amba-pl011.c
index ab025dc..e76d7d0 100644
--- a/drivers/serial/amba-pl011.c
+++ b/drivers/serial/amba-pl011.c
@@ -74,6 +74,7 @@
unsigned int lcrh_tx;
unsigned int lcrh_rx;
bool oversampling;
+ bool dma_threshold;
};
static struct vendor_data vendor_arm = {
@@ -82,6 +83,7 @@
.lcrh_tx = UART011_LCRH,
.lcrh_rx = UART011_LCRH,
.oversampling = false,
+ .dma_threshold = false,
};
static struct vendor_data vendor_st = {
@@ -90,6 +92,7 @@
.lcrh_tx = ST_UART011_LCRH_TX,
.lcrh_rx = ST_UART011_LCRH_RX,
.oversampling = true,
+ .dma_threshold = true,
};
/* Deals with DMA transactions */
@@ -527,6 +530,15 @@
/* Turn on DMA error (RX/TX will be enabled on demand) */
uap->dmacr |= UART011_DMAONERR;
writew(uap->dmacr, uap->port.membase + UART011_DMACR);
+
+ /*
+ * ST Micro variants has some specific dma burst threshold
+ * compensation. Set this to 16 bytes, so burst will only
+ * be issued above/below 16 bytes.
+ */
+ if (uap->vendor->dma_threshold)
+ writew(ST_UART011_DMAWM_RX_16 | ST_UART011_DMAWM_TX_16,
+ uap->port.membase + ST_UART011_DMAWM);
}
static void pl011_dma_shutdown(struct uart_amba_port *uap)