Accommodate uart devices with large FIFOs (or DMA buffers which amount

to the same thing) by allocating the uart(4) rx buffer based on the
device's rxfifosz rather than using a hard-coded size of 384 bytes.

The  historical 384 byte size is 3 times the largest hard-coded fifo
size in the tree, so use that ratio as a guide and allocate the buffer
as three times rxfifosz, but never smaller than the historical size.

1 files changed, 7 insertions, 1 deletions

diff --git a/sys/dev/uart/uart_core.c b/sys/dev/uart/uart_core.c
index f5a9a1c..b264e5b 100644
--- a/sys/dev/uart/uart_core.c
+++ b/sys/dev/uart/uart_core.c
@@ -457,7 +457,13 @@ uart_bus_attach(device_t dev)
 		callout_init(&sc->sc_timer, 1);
 	}
 
-	sc->sc_rxbufsz = 384;
+	/*
+	 * Ensure there is room for at least three full FIFOs of data in the
+	 * receive buffer (handles the case of low-level drivers with huge
+	 * FIFOs), and also ensure that there is no less than the historical
+	 * size of 384 bytes (handles the typical small-FIFO case).
+	 */
+	sc->sc_rxbufsz = MAX(384, sc->sc_rxfifosz * 3);
 	sc->sc_rxbuf = malloc(sc->sc_rxbufsz * sizeof(*sc->sc_rxbuf),
 	    M_UART, M_WAITOK);
 	sc->sc_txbuf = malloc(sc->sc_txfifosz * sizeof(*sc->sc_txbuf),