From:   =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>
To:     linux-serial@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>, linux-kernel@vger.kernel.org
Cc:     =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>
Subject: [PATCH 5/8] n_tty: Use DIV_ROUND_UP() in room calculation
Date:   Thu,  9 Mar 2023 10:20:32 +0200
Message-Id: <20230309082035.14880-6-ilpo.jarvinen@linux.intel.com>
In-Reply-To: <20230309082035.14880-1-ilpo.jarvinen@linux.intel.com>
References: <20230309082035.14880-1-ilpo.jarvinen@linux.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

When PARMRK is set, a character can result in up to 3 chars in the read
buffer. Receive code calculates for how many characters there (at
least) is room. Convert an opencoded rounding in the calculation to use
DIV_ROUND_UP().

Note: the room variable is decremented afterwards by one which ensures
the characters will fit into the buffer for real so the code is okay
despite rounding upwards.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
 drivers/tty/n_tty.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 2cf263de1366..6d754fc35dce 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -36,6 +36,7 @@
 #include <linux/file.h>
 #include <linux/interrupt.h>
 #include <linux/major.h>
+#include <linux/math.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/poll.h>
@@ -1692,7 +1693,7 @@ n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp,
 
 		room = N_TTY_BUF_SIZE - (ldata->read_head - tail);
 		if (I_PARMRK(tty))
-			room = (room + 2) / 3;
+			room = DIV_ROUND_UP(room, 3);
 		room--;
 		if (room <= 0) {
 			overflow = ldata->icanon && ldata->canon_head == tail;
-- 
2.30.2