diff mbox series

[U-Boot,v2,08/11] drivers: serial_sifive: Fix baud rate calculation

Message ID 20190118111820.71349-9-anup.patel@wdc.com
State Superseded
Delegated to: Andes
Headers show
Series SiFive FU540 Support | expand

Commit Message

Anup Patel Jan. 18, 2019, 11:19 a.m. UTC 
From: Atish Patra <atish.patra@wdc.com>

Compute the baud rate multipler with more precision.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
---
 drivers/serial/serial_sifive.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

Comments

Alexander Graf Jan. 18, 2019, 11:52 a.m. UTC | #1 
On 18.01.19 12:19, Anup Patel wrote:
> From: Atish Patra <atish.patra@wdc.com>
> 
> Compute the baud rate multipler with more precision.
> 
> Signed-off-by: Atish Patra <atish.patra@wdc.com>

Same here.

Alex
Anup Patel Jan. 18, 2019, 1:04 p.m. UTC | #2 
> -----Original Message-----
> From: Alexander Graf [mailto:agraf@suse.de]
> Sent: Friday, January 18, 2019 5:22 PM
> To: Anup Patel <Anup.Patel@wdc.com>; Rick Chen <rick@andestech.com>;
> Bin Meng <bmeng.cn@gmail.com>; Joe Hershberger
> <joe.hershberger@ni.com>; Lukas Auer <lukas.auer@aisec.fraunhofer.de>;
> Masahiro Yamada <yamada.masahiro@socionext.com>; Simon Glass
> <sjg@chromium.org>
> Cc: Palmer Dabbelt <palmer@sifive.com>; Paul Walmsley
> <paul.walmsley@sifive.com>; Atish Patra <Atish.Patra@wdc.com>;
> Christoph Hellwig <hch@infradead.org>; U-Boot Mailing List <u-
> boot@lists.denx.de>
> Subject: Re: [PATCH v2 08/11] drivers: serial_sifive: Fix baud rate calculation
> 
> 
> 
> On 18.01.19 12:19, Anup Patel wrote:
> > From: Atish Patra <atish.patra@wdc.com>
> >
> > Compute the baud rate multipler with more precision.
> >
> > Signed-off-by: Atish Patra <atish.patra@wdc.com>
> 
> Same here.
> 
> Alex

Sure, I will add my SoB.

Regards,
Anup
Lukas Auer Jan. 20, 2019, 8:13 p.m. UTC | #3 
On Fri, 2019-01-18 at 11:19 +0000, Anup Patel wrote:
> From: Atish Patra <atish.patra@wdc.com>
> 
> Compute the baud rate multipler with more precision.
> 
> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> Reviewed-by: Alexander Graf <agraf@suse.de>
> ---
>  drivers/serial/serial_sifive.c | 28 ++++++++++++++++++++++++++--
>  1 file changed, 26 insertions(+), 2 deletions(-)
> 

Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
diff mbox series

Patch

diff --git a/drivers/serial/serial_sifive.c b/drivers/serial/serial_sifive.c
index 341728a690..ea4d35d48c 100644
--- a/drivers/serial/serial_sifive.c
+++ b/drivers/serial/serial_sifive.c
@@ -33,16 +33,40 @@  struct uart_sifive {
 };
 
 struct sifive_uart_platdata {
-	unsigned int clock;
+	unsigned long clock;
 	int saved_input_char;
 	struct uart_sifive *regs;
 };
 
+/**
+ * Find minimum divisor divides in_freq to max_target_hz;
+ * Based on uart driver n SiFive FSBL.
+ *
+ * f_baud = f_in / (div + 1) => div = (f_in / f_baud) - 1
+ * The nearest integer solution requires rounding up as to not exceed
+ * max_target_hz.
+ * div  = ceil(f_in / f_baud) - 1
+ *	= floor((f_in - 1 + f_baud) / f_baud) - 1
+ * This should not overflow as long as (f_in - 1 + f_baud) does not exceed
+ * 2^32 - 1, which is unlikely since we represent frequencies in kHz.
+ */
+static inline unsigned int uart_min_clk_divisor(unsigned long in_freq,
+						unsigned long max_target_hz)
+{
+	unsigned long quotient =
+			(in_freq + max_target_hz - 1) / (max_target_hz);
+	/* Avoid underflow */
+	if (quotient == 0)
+		return 0;
+	else
+		return quotient - 1;
+}
+
 /* Set up the baud rate in gd struct */
 static void _sifive_serial_setbrg(struct uart_sifive *regs,
 				  unsigned long clock, unsigned long baud)
 {
-	writel((u32)((clock / baud) - 1), &regs->div);
+	writel((uart_min_clk_divisor(clock, baud)), &regs->div);
 }
 
 static void _sifive_serial_init(struct uart_sifive *regs)