From: Masahiro Yamada <yamada.masahiro@socionext.com> To: linux-serial@vger.kernel.org Cc: Denys Vlasenko <dvlasenk@redhat.com>, Masahiro Yamada <yamada.masahiro@socionext.com>, Jiri Slaby <jslaby@suse.com>, linux-kernel@vger.kernel.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, linux-arm-kernel@lists.infradead.org Subject: [PATCH 4/4] serial: 8250_uniphier: avoid locking for FCR register write Date: Mon, 24 Oct 2016 17:00:30 +0900 [thread overview] Message-ID: <1477296030-7517-5-git-send-email-yamada.masahiro@socionext.com> (raw) In-Reply-To: <1477296030-7517-1-git-send-email-yamada.masahiro@socionext.com> The hardware book says, the FCR is combined with a register called CHAR (it will trigger interrupt when a specific character is received). At first, I used lock/read/modify/write/unlock dance for the FCR to not affect the upper bits, but the CHAR is actually never used. It should not hurt to always clear the CHAR and to handle the FCR as a normal case. It can save the costly locking. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Suggested-by: Denys Vlasenko <dvlasenk@redhat.com> --- drivers/tty/serial/8250/8250_uniphier.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/8250/8250_uniphier.c b/drivers/tty/serial/8250/8250_uniphier.c index 92e7bb7..746680e 100644 --- a/drivers/tty/serial/8250/8250_uniphier.c +++ b/drivers/tty/serial/8250/8250_uniphier.c @@ -101,7 +101,7 @@ static unsigned int uniphier_serial_in(struct uart_port *p, int offset) static void uniphier_serial_out(struct uart_port *p, int offset, int value) { unsigned int valshift = 0; - bool normal = false; + bool normal = true; switch (offset) { case UART_FCR: @@ -114,9 +114,9 @@ static void uniphier_serial_out(struct uart_port *p, int offset, int value) /* fall through */ case UART_MCR: offset = UNIPHIER_UART_LCR_MCR; + normal = false; break; default: - normal = true; offset <<= UNIPHIER_UART_REGSHIFT; break; } -- 1.9.1
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From: yamada.masahiro@socionext.com (Masahiro Yamada) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 4/4] serial: 8250_uniphier: avoid locking for FCR register write Date: Mon, 24 Oct 2016 17:00:30 +0900 [thread overview] Message-ID: <1477296030-7517-5-git-send-email-yamada.masahiro@socionext.com> (raw) In-Reply-To: <1477296030-7517-1-git-send-email-yamada.masahiro@socionext.com> The hardware book says, the FCR is combined with a register called CHAR (it will trigger interrupt when a specific character is received). At first, I used lock/read/modify/write/unlock dance for the FCR to not affect the upper bits, but the CHAR is actually never used. It should not hurt to always clear the CHAR and to handle the FCR as a normal case. It can save the costly locking. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Suggested-by: Denys Vlasenko <dvlasenk@redhat.com> --- drivers/tty/serial/8250/8250_uniphier.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/8250/8250_uniphier.c b/drivers/tty/serial/8250/8250_uniphier.c index 92e7bb7..746680e 100644 --- a/drivers/tty/serial/8250/8250_uniphier.c +++ b/drivers/tty/serial/8250/8250_uniphier.c @@ -101,7 +101,7 @@ static unsigned int uniphier_serial_in(struct uart_port *p, int offset) static void uniphier_serial_out(struct uart_port *p, int offset, int value) { unsigned int valshift = 0; - bool normal = false; + bool normal = true; switch (offset) { case UART_FCR: @@ -114,9 +114,9 @@ static void uniphier_serial_out(struct uart_port *p, int offset, int value) /* fall through */ case UART_MCR: offset = UNIPHIER_UART_LCR_MCR; + normal = false; break; default: - normal = true; offset <<= UNIPHIER_UART_REGSHIFT; break; } -- 1.9.1
next prev parent reply other threads:[~2016-10-24 7:59 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-10-24 8:00 [PATCH 0/4] serial: 8250_uniphier: some fixes and optimization Masahiro Yamada 2016-10-24 8:00 ` Masahiro Yamada 2016-10-24 8:00 ` [PATCH 1/4] serial: 8250_uniphier: fix more unterminated string Masahiro Yamada 2016-10-24 8:00 ` Masahiro Yamada 2016-10-24 8:00 ` [PATCH 2/4] serial: 8250_uniphier: fix clearing divisor latch access bit Masahiro Yamada 2016-10-24 8:00 ` Masahiro Yamada 2016-10-24 8:00 ` [PATCH 3/4] serial: 8250_uniphier: hardcode regshift to avoid unneeded memory read Masahiro Yamada 2016-10-24 8:00 ` Masahiro Yamada 2016-10-24 8:00 ` Masahiro Yamada [this message] 2016-10-24 8:00 ` [PATCH 4/4] serial: 8250_uniphier: avoid locking for FCR register write Masahiro Yamada
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