| Message ID | 1431438266-28094-1-git-send-email-Dave.Martin@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 12 May 2015 14:44:26 +0100, Dave Martin wrote: > This will cause a conflict with tty-next because it pulls forward > some changes made by commit 1e84d22 (serial/amba-pl011: Refactor and > simplify TX FIFO handling); however, the resolution is simple except > for the following lines which may need to be deleted manually from > amba-pl011.c:pl011_startup(): By resolution is simple you mean: keep the code as it is in tty-next, right?
On Tue, May 12, 2015 at 03:00:27PM +0100, Jakub Kici?ski wrote: > On Tue, 12 May 2015 14:44:26 +0100, Dave Martin wrote: > > This will cause a conflict with tty-next because it pulls forward > > some changes made by commit 1e84d22 (serial/amba-pl011: Refactor and > > simplify TX FIFO handling); however, the resolution is simple except > > for the following lines which may need to be deleted manually from > > amba-pl011.c:pl011_startup(): > > By resolution is simple you mean: keep the code as it is in tty-next, > right? Yes, that's right. Cheers ---Dave
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 6f5a072..763eb20 100644 --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -1249,20 +1249,19 @@ __acquires(&uap->port.lock) /* * Transmit a character - * There must be at least one free entry in the TX FIFO to accept the char. * - * Returns true if the FIFO might have space in it afterwards; - * returns false if the FIFO definitely became full. + * Returns true if the character was successfully queued to the FIFO. + * Returns false otherwise. */ static bool pl011_tx_char(struct uart_amba_port *uap, unsigned char c) { + if (readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF) + return false; /* unable to transmit character */ + writew(c, uap->port.membase + UART01x_DR); uap->port.icount.tx++; - if (likely(uap->tx_irq_seen > 1)) - return true; - - return !(readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF); + return true; } static bool pl011_tx_chars(struct uart_amba_port *uap) @@ -1296,7 +1295,8 @@ static bool pl011_tx_chars(struct uart_amba_port *uap) return false; if (uap->port.x_char) { - pl011_tx_char(uap, uap->port.x_char); + if (!pl011_tx_char(uap, uap->port.x_char)) + goto done; uap->port.x_char = 0; --count; }
Commit 734745caeb9f155ab58918834a8c70e83fa6afd3 serial/amba-pl011: (Activate TX IRQ passively) introduces a race which causes the driver sometimes to attempt to write a character to the TX FIFO when the FIFO is already full. The PL011 does not guarantee its behaviour when the FIFO is overfilled. In practice, this can cause duplicate and/or dropped characters to be output on the wire. The problem is common enough to be readily observable on the ARM Juno platform when the PL011 UART is used as the console and DMA is not in use. This patch fixes this problem by always polling for space before each character is written to the FIFO. This will be amended to a less brute-force approach in a later commit, but this patch should help ensure correct behaviour for now. Signed-off-by: Dave Martin <Dave.Martin@arm.com> --- The patch is based on gregkh/tty.git tty-linus. Please consider applying it for v4.1. Without it, we have a regression compared with v4.0. *Note* This will cause a conflict with tty-next because it pulls forward some changes made by commit 1e84d22 (serial/amba-pl011: Refactor and simplify TX FIFO handling); however, the resolution is simple except for the following lines which may need to be deleted manually from amba-pl011.c:pl011_startup(): -8<- /* Assume that TX IRQ doesn't work until we see one: */ uap->tx_irq_seen = 0; ->8- (This is is the same mismerge already observed by Steven Rothwell when building next.) Cheers ---Dave drivers/tty/serial/amba-pl011.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)