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ARM: PL011: add DMA burst threshold support for ST variants

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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 <[email protected]>
Signed-off-by: Russell King <[email protected]>
This commit is contained in:
Russell King 2010-12-22 17:59:16 +00:00
commit 38d624361b
2 changed files with 27 additions and 0 deletions
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12
drivers/serial/amba-pl011.c
View file

@ -74,6 +74,7 @@ struct vendor_data {
unsigned int lcrh_tx;
unsigned int lcrh_rx;
bool oversampling;
bool dma_threshold;
};
static struct vendor_data vendor_arm = {
@ -82,6 +83,7 @@ static struct vendor_data vendor_arm = {
.lcrh_tx = UART011_LCRH,
.lcrh_rx = UART011_LCRH,
.oversampling = false,
.dma_threshold = false,
};
static struct vendor_data vendor_st = {
@ -90,6 +92,7 @@ static struct vendor_data vendor_st = {
.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 @@ static void pl011_dma_startup(struct uart_amba_port *uap)
/* 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)