linux-kernel - [PATCH v2 1/2] serial: dz: xmit buffer is UART_XMIT

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Date:   Thu, 25 Aug 2022 16:17:45 +0300
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org,
        "Maciej W . Rozycki" <macro@...am.me.uk>,
        linux-kernel@...r.kernel.org
Cc:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: [PATCH v2 1/2] serial: dz: xmit buffer is UART_XMIT_SIZE'd

Instead of DZ_XMIT_SIZE, use the normal UART_XMIT_SIZE directly as it's
the correct size of the xmit circular buffer.

In theory, the Tx code would be buggy if UART_XMIT_SIZE differs from
4096 (occurs when PAGE_SIZE > 4k), however, given the lack of issue
reports such configuration likely doesn't occur with any real platform
with dz HW. The inconsisted sizes would cause missing characters and
never-ending bogus Tx when ->head reaches the region above 4k. The
issue, if it would be real, would predate git days.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
---
 drivers/tty/serial/dz.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/dz.c b/drivers/tty/serial/dz.c
index 2e21acf39720..5d2588f3e6a9 100644
--- a/drivers/tty/serial/dz.c
+++ b/drivers/tty/serial/dz.c
@@ -279,7 +279,7 @@ static inline void dz_transmit_chars(struct dz_mux *mux)
 	 * so we go one char at a time) :-<
 	 */
 	tmp = xmit->buf[xmit->tail];
-	xmit->tail = (xmit->tail + 1) & (DZ_XMIT_SIZE - 1);
+	xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
 	dz_out(dport, DZ_TDR, tmp);
 	dport->port.icount.tx++;

-- 
2.30.2