[PATCH] spi: rspi: Increase accuracy of bit rate for RZ

[PATCH] spi: rspi: Increase accuracy of bit rate for RZ

[Chris Brandt]

When you leave the clock divider at 0, 130kHz is the lowest you can go.
Also, by adjusting the clock divider you can get more accurate resolutions
for clock speeds lower than 16MHz. This patch uses the clock divider as
part of the bit rate setup.

Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
---
 drivers/spi/spi-rspi.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c
index 8188433..a816f07 100644
--- a/drivers/spi/spi-rspi.c
+++ b/drivers/spi/spi-rspi.c
@@ -295,14 +295,24 @@ static int rspi_set_config_register(struct rspi_data *rspi, int access_size)
 static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size)
 {
 	int spbr;
+	int div = 0;
+	unsigned long clksrc;
 
 	/* Sets output mode, MOSI signal, and (optionally) loopback */
 	rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR);
 
+	clksrc = clk_get_rate(rspi->clk);
+	while (div < 3) {
+		if (rspi->max_speed_hz >= clksrc/4) /* 4=(CLK/2)/2 */
+			break;
+		div++;
+		clksrc /= 2;
+	}
+
 	/* Sets transfer bit rate */
-	spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk),
-			    2 * rspi->max_speed_hz) - 1;
+	spbr = DIV_ROUND_UP(clksrc, 2 * rspi->max_speed_hz) - 1;
 	rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR);
+	rspi->spcmd |= div << 2;
 
 	/* Disable dummy transmission, set byte access */
 	rspi_write8(rspi, SPDCR_SPLBYTE, RSPI_SPDCR);
-- 
1.9.1

Applied "spi: rspi: Increase accuracy of bit rate for RZ" to the spi tree

[Mark Brown]

The patch

   spi: rspi: Increase accuracy of bit rate for RZ

has been applied to the spi tree at

   git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From ed66b659f95717432b7ede24efd8b2a34f479d32 Mon Sep 17 00:00:00 2001
From: Chris Brandt <chris.brandt@renesas.com>
Date: Fri, 5 Aug 2016 09:36:03 -0400
Subject: [PATCH] spi: rspi: Increase accuracy of bit rate for RZ

When you leave the clock divider at 0, 130kHz is the lowest you can go.
Also, by adjusting the clock divider you can get more accurate resolutions
for clock speeds lower than 16MHz. This patch uses the clock divider as
part of the bit rate setup.

Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 drivers/spi/spi-rspi.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c
index 818843336932..a816f07e168e 100644
--- a/drivers/spi/spi-rspi.c
+++ b/drivers/spi/spi-rspi.c
@@ -295,14 +295,24 @@ static int rspi_set_config_register(struct rspi_data *rspi, int access_size)
 static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size)
 {
 	int spbr;
+	int div = 0;
+	unsigned long clksrc;
 
 	/* Sets output mode, MOSI signal, and (optionally) loopback */
 	rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR);
 
+	clksrc = clk_get_rate(rspi->clk);
+	while (div < 3) {
+		if (rspi->max_speed_hz >= clksrc/4) /* 4=(CLK/2)/2 */
+			break;
+		div++;
+		clksrc /= 2;
+	}
+
 	/* Sets transfer bit rate */
-	spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk),
-			    2 * rspi->max_speed_hz) - 1;
+	spbr = DIV_ROUND_UP(clksrc, 2 * rspi->max_speed_hz) - 1;
 	rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR);
+	rspi->spcmd |= div << 2;
 
 	/* Disable dummy transmission, set byte access */
 	rspi_write8(rspi, SPDCR_SPLBYTE, RSPI_SPDCR);
-- 
2.8.1

Re: [PATCH] spi: rspi: Increase accuracy of bit rate for RZ

[Geert Uytterhoeven]

Hi Chris,

On Fri, Aug 5, 2016 at 3:36 PM, Chris Brandt <chris.brandt-zM6kxYcvzFBBDgjK7y7TUQ@public.gmane.org> wrote:
> When you leave the clock divider at 0, 130kHz is the lowest you can go.
> Also, by adjusting the clock divider you can get more accurate resolutions
> for clock speeds lower than 16MHz. This patch uses the clock divider as
> part of the bit rate setup.
>
> Signed-off-by: Chris Brandt <chris.brandt-zM6kxYcvzFBBDgjK7y7TUQ@public.gmane.org>
> ---
>  drivers/spi/spi-rspi.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c
> index 8188433..a816f07 100644
> --- a/drivers/spi/spi-rspi.c
> +++ b/drivers/spi/spi-rspi.c
> @@ -295,14 +295,24 @@ static int rspi_set_config_register(struct rspi_data *rspi, int access_size)
>  static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size)
>  {
>         int spbr;
> +       int div = 0;
> +       unsigned long clksrc;
>
>         /* Sets output mode, MOSI signal, and (optionally) loopback */
>         rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR);
>
> +       clksrc = clk_get_rate(rspi->clk);
> +       while (div < 3) {
> +               if (rspi->max_speed_hz >= clksrc/4) /* 4=(CLK/2)/2 */
> +                       break;
> +               div++;
> +               clksrc /= 2;
> +       }
> +
>         /* Sets transfer bit rate */
> -       spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk),
> -                           2 * rspi->max_speed_hz) - 1;
> +       spbr = DIV_ROUND_UP(clksrc, 2 * rspi->max_speed_hz) - 1;
>         rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR);
> +       rspi->spcmd |= div << 2;
>
>         /* Disable dummy transmission, set byte access */
>         rspi_write8(rspi, SPDCR_SPLBYTE, RSPI_SPDCR);

I believe this applies not only to RZ, but to all other supported RSPI variants?
Hence I think it should be made common.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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RE: [PATCH] spi: rspi: Increase accuracy of bit rate for RZ

[Chris Brandt]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 945 bytes --]

Hi Geert,

On Mon, Aug 29, 2016, Geert Uytterhoeven wrote:
> I believe this applies not only to RZ, but to all other supported RSPI variants?
> Hence I think it should be made common.

I would think it would be the same for all the other parts with RSPI.

Currently there are 3 separate config functions:
 - rspi_set_config_register
 - rspi_rz_set_config_register
 - qspi_set_config_register

By "common", do you mean:
A) add the same code to each of the other 2 functions?
     (ie, common functionality for all device)

B) make some new function/macro that all config functions call?
     (ie, same code for setting the register bits)


Note: I only really have a RZ/A platform, so I can't really test it on any other devices (other than just looking in the hardware manuals)

Chris


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