by Wolfram Sang

[permalink] [raw]

Subject: Re: [PATCH REBASE] i2c-designware: make SDA hold time configurable

On Tue, May 14, 2013 at 03:04:02PM +0200, Christian Ruppert wrote:
> This patch makes the SDA hold time configurable through device tree.
>
> [rebased to i2c-current/i2c-next/mainline-3.10-rc1]
>
> Signed-off-by: Christian Ruppert <[email protected]>
> Signed-off-by: Pierrick Hascoet <[email protected]>

Hmm, I really have problems adding a generic property. I need to better
understand why this is needed? What is the usecase? Can't a safe value
be calculated depending on the bus-speed? Is there a public datasheet
available somewhere?

Thanks,

Wolfram

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2013-06-12 14:48:44

Hi,

On Wed, Jun 12, 2013 at 04:47:45PM +0200, Christian Ruppert wrote:
> On Mon, Jun 10, 2013 at 05:29:55PM +0200, Wolfram Sang wrote:
> > On Tue, May 14, 2013 at 03:04:02PM +0200, Christian Ruppert wrote:
> > > This patch makes the SDA hold time configurable through device tree.
> > >
> > > [rebased to i2c-current/i2c-next/mainline-3.10-rc1]
> > >
> > > Signed-off-by: Christian Ruppert <[email protected]>
> > > Signed-off-by: Pierrick Hascoet <[email protected]>
> >
> > Hmm, I really have problems adding a generic property. I need to better
> > understand why this is needed? What is the usecase? Can't a safe value
> > be calculated depending on the bus-speed? Is there a public datasheet
> > available somewhere?
>
> I checked with our PCB/Applications team and the data sheets for the
> peripherals in question (DVB demodulator front ends) are under NDA.
> Mika, you seem to be interested in this patch as well. Do you know of
> any publicly available data sheets for hardware requiring this
> adjustment?

So, I looked around and found:
http://www.maximintegrated.com/app-notes/index.mvp/id/3268

which after thinking further about it gives me the following
conclusions:

- sda-hold-time is a property/requirement of a device not following
the I2C spec. It is not a property of the master!

- It should not be encoded in the devicetree, since the flaw is implicit
to the device, so only the driver needs to know about it. I wonder
about something like this in the i2c slave driver:

ret = i2c_request_sda_hold_time(client);

The core then can collect the requests and forward them to the host
driver. This driver then can set up the hardware or return -EOPNOTSUPP
and we can even warn the user that there might be problems ahead.

- I wonder if we really need to have a parameter time-in-ns? The
specs cleary say 300ns, so I'd think this is the value we should
always use. This is from a theorhetical pov though, maybe your
practical experience is different. What values do you need?

> In the case of the Designware block, the parameter both changes SDA and
> START hold times, however, and you'll find lots of data sheets for
> hardware with START hold time requirements on the net, e.g.
> http://ww1.microchip.com/downloads/en/DeviceDoc/21805B.pdf

What I couldn't find is a reference manual for a designware IP that
supports sda hold time? I found some spear SoC which do not have that
register, so that should surely be reflected in the patchset, too.

> The empirical solution in the function i2c_dw_scl_hcnt does not seem to
> work in all cases: Our lab guys confirmed that we have several PCB
> designs which do not work without adjusting the sda-hold-time parameter
> to an appropriate value. The value seems to be different for different
> PCBs.

I'd hope that 300ns is a safe value for all PCBs?

> I suspect that this kind of configurability is not the same for all i2c
> bus master hardware.

Yeah, maybe some do sda-holding by default? Dunno, never checked for
that detail.

Regards,

Wolfram

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2013-06-19 13:59:49

by Christian Ruppert

This patch makes the SDA hold time configurable through device tree.

Signed-off-by: Christian Ruppert <[email protected]>
Signed-off-by: Pierrick Hascoet <[email protected]>
---
.../devicetree/bindings/i2c/i2c-designware.txt | 14 ++++++++++++++
arch/arc/boot/dts/abilis_tb100_dvk.dts | 10 +++++-----
arch/arc/boot/dts/abilis_tb101_dvk.dts | 10 +++++-----
drivers/i2c/busses/i2c-designware-core.c | 13 +++++++++++++
drivers/i2c/busses/i2c-designware-core.h | 1 +
drivers/i2c/busses/i2c-designware-platdrv.c | 10 ++++++++++
6 files changed, 48 insertions(+), 10 deletions(-)

diff --git a/Documentation/devicetree/bindings/i2c/i2c-designware.txt b/Documentation/devicetree/bindings/i2c/i2c-designware.txt
index e42a2ee..3266cc7 100644
--- a/Documentation/devicetree/bindings/i2c/i2c-designware.txt
+++ b/Documentation/devicetree/bindings/i2c/i2c-designware.txt
@@ -10,6 +10,9 @@ Recommended properties :

- clock-frequency : desired I2C bus clock frequency in Hz.

+Optional properties :
+ - i2c-sda-hold-time-ns : should contain the SDA hold time in nanoseconds.
+
Example :

i2c@f0000 {
@@ -20,3 +23,14 @@ Example :
interrupts = <11>;
clock-frequency = <400000>;
};
+
+ i2c@1120000 {
+ #address-cells = <1>;
+ #size-cells = <0>;
+ compatible = "snps,designware-i2c";
+ reg = <0x1120000 0x1000>;
+ interrupt-parent = <&ictl>;
+ interrupts = <12 1>;
+ clock-frequency = <400000>;
+ i2c-sda-hold-time-ns = <300>;
+ };
diff --git a/arch/arc/boot/dts/abilis_tb100_dvk.dts b/arch/arc/boot/dts/abilis_tb100_dvk.dts
index 0fa0d4a..ebc313a 100644
--- a/arch/arc/boot/dts/abilis_tb100_dvk.dts
+++ b/arch/arc/boot/dts/abilis_tb100_dvk.dts
@@ -45,19 +45,19 @@
};

i2c0: i2c@FF120000 {
- sda-hold-time = <432>;
+ i2c-sda-hold-time-ns = <432>;
};
i2c1: i2c@FF121000 {
- sda-hold-time = <432>;
+ i2c-sda-hold-time-ns = <432>;
};
i2c2: i2c@FF122000 {
- sda-hold-time = <432>;
+ i2c-sda-hold-time-ns = <432>;
};
i2c3: i2c@FF123000 {
- sda-hold-time = <432>;
+ i2c-sda-hold-time-ns = <432>;
};
i2c4: i2c@FF124000 {
- sda-hold-time = <432>;
+ i2c-sda-hold-time-ns = <432>;
};

leds {
diff --git a/arch/arc/boot/dts/abilis_tb101_dvk.dts b/arch/arc/boot/dts/abilis_tb101_dvk.dts
index a4d80ce..b204657 100644
--- a/arch/arc/boot/dts/abilis_tb101_dvk.dts
+++ b/arch/arc/boot/dts/abilis_tb101_dvk.dts
@@ -45,19 +45,19 @@
};

i2c0: i2c@FF120000 {
- sda-hold-time = <432>;
+ i2c-sda-hold-time-ns = <432>;
};
i2c1: i2c@FF121000 {
- sda-hold-time = <432>;
+ i2c-sda-hold-time-ns = <432>;
};
i2c2: i2c@FF122000 {
- sda-hold-time = <432>;
+ i2c-sda-hold-time-ns = <432>;
};
i2c3: i2c@FF123000 {
- sda-hold-time = <432>;
+ i2c-sda-hold-time-ns = <432>;
};
i2c4: i2c@FF124000 {
- sda-hold-time = <432>;
+ i2c-sda-hold-time-ns = <432>;
};

leds {
diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
index c41ca63..66119e2 100644
--- a/drivers/i2c/busses/i2c-designware-core.c
+++ b/drivers/i2c/busses/i2c-designware-core.c
@@ -67,9 +67,12 @@
#define DW_IC_STATUS 0x70
#define DW_IC_TXFLR 0x74
#define DW_IC_RXFLR 0x78
+#define DW_IC_SDA_HOLD 0x7c
#define DW_IC_TX_ABRT_SOURCE 0x80
#define DW_IC_ENABLE_STATUS 0x9c
#define DW_IC_COMP_PARAM_1 0xf4
+#define DW_IC_COMP_VERSION 0xf8
+#define DW_IC_SDA_HOLD_MIN_VERS 0x3131312A
#define DW_IC_COMP_TYPE 0xfc
#define DW_IC_COMP_TYPE_VALUE 0x44570140

@@ -332,6 +335,16 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
dw_writel(dev, lcnt, DW_IC_FS_SCL_LCNT);
dev_dbg(dev->dev, "Fast-mode HCNT:LCNT = %d:%d\n", hcnt, lcnt);

+ /* Configure SDA Hold Time if required */
+ reg = dw_readl(dev, DW_IC_COMP_VERSION);
+ if (dev->sda_hold_time) {
+ if (reg >= DW_IC_SDA_HOLD_MIN_VERS)
+ dw_writel(dev, dev->sda_hold_time, DW_IC_SDA_HOLD);
+ else
+ dev_warn(dev->dev,
+ "Hardware too old to adjust SDA hold time.");
+ }
+
/* Configure Tx/Rx FIFO threshold levels */
dw_writel(dev, dev->tx_fifo_depth - 1, DW_IC_TX_TL);
dw_writel(dev, 0, DW_IC_RX_TL);
diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
index e761ad1..912aa22 100644
--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/drivers/i2c/busses/i2c-designware-core.h
@@ -90,6 +90,7 @@ struct dw_i2c_dev {
unsigned int tx_fifo_depth;
unsigned int rx_fifo_depth;
int rx_outstanding;
+ u32 sda_hold_time;
};

#define ACCESS_SWAP 0x00000001
diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index 35b70a1..8b9d3f1 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -34,6 +34,7 @@
#include <linux/sched.h>
#include <linux/err.h>
#include <linux/interrupt.h>
+#include <linux/of.h>
#include <linux/of_i2c.h>
#include <linux/platform_device.h>
#include <linux/pm.h>
@@ -121,6 +122,15 @@ static int dw_i2c_probe(struct platform_device *pdev)
return PTR_ERR(dev->clk);
clk_prepare_enable(dev->clk);

+ if (pdev->dev.of_node) {
+ u32 ht = 0;
+ u32 ic_clk = dev->get_clk_rate_khz(dev);
+
+ of_property_read_u32(pdev->dev.of_node,
+ "i2c-sda-hold-time-ns", &ht);
+ dev->sda_hold_time = ((u64)ic_clk * ht + 500000) / 1000000;
+ }
+
dev->functionality =
I2C_FUNC_I2C |
I2C_FUNC_10BIT_ADDR |
--
1.7.1

2013-06-25 16:39:26

[permalink] [raw]

On Wednesday 03 July 2013, Stehle Vincent-B46079 wrote:
> > From: Christian Ruppert [mailto:[email protected]]
> (..)
> > Although this doesn't explicitly state what the function returns to me
> > this sounds more like the quotient is returned rather than the remainder?
>
> Hi,
>
> Yes div_u64() returns the quotient.
>
> It is defined in linux/math64.h as:
>
> static inline u64 div_u64(u64 dividend, u32 divisor)
> {
> u32 remainder;
> return div_u64_rem(dividend, divisor, &remainder);
> }
>
> The remainder is probably fully optimized out.

Ah, you are right, sorry for the confusion on my part.

I thought you had used do_div() rather than div_u64().
Everything's fine then, feel free to add my

Acked-by: Arnd Bergmann <[email protected]>

to your patch.

Arnd