[U-Boot] [PATCH] i2c: mvtwsi: Fix problem with baud rate calculation
The current implementation for baudrate calculation is incorrect. This part from the formula:
"2 ^ (n + 1)" is not equivalent to (1 << n) but to (2 << n)!
This patch fixes this and moves this calculation to a function instead of using a macro. This new function is taken from the Linux kernel.
This was detected and tested on the Marvell Armada A38x DB-88F6820-GP eval board.
Signed-off-by: Stefan Roese sr@denx.de Cc: Prafulla Wadaskar prafulla@marvell.com Cc: Luka Perkov luka.perkov@sartura.hr Cc: Hans de Goede hdegoede@redhat.com Cc: Ian Campbell ijc@hellion.org.uk Cc: Heiko Schocher hs@denx.de --- drivers/i2c/mvtwsi.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/drivers/i2c/mvtwsi.c b/drivers/i2c/mvtwsi.c index 9b2ca1e..320235c 100644 --- a/drivers/i2c/mvtwsi.c +++ b/drivers/i2c/mvtwsi.c @@ -228,13 +228,10 @@ static int twsi_stop(int status) return status; }
-/* - * Ugly formula to convert m and n values to a frequency comes from - * TWSI specifications - */ - -#define TWSI_FREQUENCY(m, n) \ - (CONFIG_SYS_TCLK / (10 * (m + 1) * (1 << n))) +static unsigned int twsi_calc_freq(const int n, const int m) +{ + return CONFIG_SYS_TCLK / (10 * (m + 1) * (2 << n)); +}
/* * Reset controller. @@ -266,7 +263,7 @@ static unsigned int twsi_i2c_set_bus_speed(struct i2c_adapter *adap, /* compute m, n setting for highest speed not above requested speed */ for (n = 0; n < 8; n++) { for (m = 0; m < 16; m++) { - tmp_speed = TWSI_FREQUENCY(m, n); + tmp_speed = twsi_calc_freq(n, m); if ((tmp_speed <= requested_speed) && (tmp_speed > highest_speed)) { highest_speed = tmp_speed;
Hi,
On 17-03-15 11:08, Stefan Roese wrote:
The current implementation for baudrate calculation is incorrect. This part from the formula:
"2 ^ (n + 1)" is not equivalent to (1 << n) but to (2 << n)!
This patch fixes this and moves this calculation to a function instead of using a macro.
Hmm, this does not match with what the Allwinner datasheets say: https://github.com/allwinner-zh/documents/blob/master/A20/A20%20user%20manua...
They say:
Fsamp = F 0 = Fin / 2^CLK_N F1 = F0 / (CLK_M + 1) Foscl = F1 / 10 = Fin / (2^CLK_N * (CLK_M + 1)*10)
With Foscl being the ultimate i2c speed. Notice that they are talking about 2 ^ CLK_N not 2 ^ (CLK_N + 1)
And they have a few examples which match this. Now it could be that a register value of 0 means CLK_N = 1, reg 1 CLK_N = 2, etc. this is not clearly specified ...
This new function is taken from the Linux kernel.
Interesting, because on Allwinnner / sunxi devices we are using the kernel driver formula unmodified, and things seem to work fine despite this. Could be tolerances allowing this, could be the Allwinner datasheet being unclear.
I've send allwinner a mail asking them to clarify this.
This was detected and tested on the Marvell Armada A38x DB-88F6820-GP eval board.
So I take it you connected a memory oscilloscope to the i2c wires ?
Regards,
Hans
Signed-off-by: Stefan Roese sr@denx.de Cc: Prafulla Wadaskar prafulla@marvell.com Cc: Luka Perkov luka.perkov@sartura.hr Cc: Hans de Goede hdegoede@redhat.com Cc: Ian Campbell ijc@hellion.org.uk Cc: Heiko Schocher hs@denx.de
drivers/i2c/mvtwsi.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/drivers/i2c/mvtwsi.c b/drivers/i2c/mvtwsi.c index 9b2ca1e..320235c 100644 --- a/drivers/i2c/mvtwsi.c +++ b/drivers/i2c/mvtwsi.c @@ -228,13 +228,10 @@ static int twsi_stop(int status) return status; }
-/*
- Ugly formula to convert m and n values to a frequency comes from
- TWSI specifications
- */
-#define TWSI_FREQUENCY(m, n) \
- (CONFIG_SYS_TCLK / (10 * (m + 1) * (1 << n)))
+static unsigned int twsi_calc_freq(const int n, const int m) +{
- return CONFIG_SYS_TCLK / (10 * (m + 1) * (2 << n));
+}
/*
- Reset controller.
@@ -266,7 +263,7 @@ static unsigned int twsi_i2c_set_bus_speed(struct i2c_adapter *adap, /* compute m, n setting for highest speed not above requested speed */ for (n = 0; n < 8; n++) { for (m = 0; m < 16; m++) {
tmp_speed = TWSI_FREQUENCY(m, n);
tmp_speed = twsi_calc_freq(n, m); if ((tmp_speed <= requested_speed) && (tmp_speed > highest_speed)) { highest_speed = tmp_speed;
Hi Hans,
On 17.03.2015 12:15, Hans de Goede wrote:
On 17-03-15 11:08, Stefan Roese wrote:
The current implementation for baudrate calculation is incorrect. This part from the formula:
"2 ^ (n + 1)" is not equivalent to (1 << n) but to (2 << n)!
This patch fixes this and moves this calculation to a function instead of using a macro.
Hmm, this does not match with what the Allwinner datasheets say: https://github.com/allwinner-zh/documents/blob/master/A20/A20%20user%20manua...
They say:
Fsamp = F 0 = Fin / 2^CLK_N F1 = F0 / (CLK_M + 1) Foscl = F1 / 10 = Fin / (2^CLK_N * (CLK_M + 1)*10)
With Foscl being the ultimate i2c speed. Notice that they are talking about 2 ^ CLK_N not 2 ^ (CLK_N + 1)
And they have a few examples which match this. Now it could be that a register value of 0 means CLK_N = 1, reg 1 CLK_N = 2, etc. this is not clearly specified ...
This new function is taken from the Linux kernel.
Interesting, because on Allwinnner / sunxi devices we are using the kernel driver formula unmodified, and things seem to work fine despite this. Could be tolerances allowing this, could be the Allwinner datasheet being unclear.
I've send allwinner a mail asking them to clarify this.
Good.
Here the complete formula from the A38x manual:
F_SCL = F_TCLK / (10 * (M + 1) * 2 ^ (N + 1))
This was detected and tested on the Marvell Armada A38x DB-88F6820-GP eval board.
So I take it you connected a memory oscilloscope to the i2c wires ?
No. I noticed that I2C doesn't work on this board with the current code. And checked for differences to the Linux code. And with this change, I2C does work on this board.
Thanks, Stefan
Hi,
On 17-03-15 12:25, Stefan Roese wrote:
Hi Hans,
On 17.03.2015 12:15, Hans de Goede wrote:
On 17-03-15 11:08, Stefan Roese wrote:
The current implementation for baudrate calculation is incorrect. This part from the formula:
"2 ^ (n + 1)" is not equivalent to (1 << n) but to (2 << n)!
This patch fixes this and moves this calculation to a function instead of using a macro.
Hmm, this does not match with what the Allwinner datasheets say: https://github.com/allwinner-zh/documents/blob/master/A20/A20%20user%20manua...
They say:
Fsamp = F 0 = Fin / 2^CLK_N F1 = F0 / (CLK_M + 1) Foscl = F1 / 10 = Fin / (2^CLK_N * (CLK_M + 1)*10)
With Foscl being the ultimate i2c speed. Notice that they are talking about 2 ^ CLK_N not 2 ^ (CLK_N + 1)
And they have a few examples which match this. Now it could be that a register value of 0 means CLK_N = 1, reg 1 CLK_N = 2, etc. this is not clearly specified ...
This new function is taken from the Linux kernel.
Interesting, because on Allwinnner / sunxi devices we are using the kernel driver formula unmodified, and things seem to work fine despite this. Could be tolerances allowing this, could be the Allwinner datasheet being unclear.
I've send allwinner a mail asking them to clarify this.
Good.
Here the complete formula from the A38x manual:
F_SCL = F_TCLK / (10 * (M + 1) * 2 ^ (N + 1))
This was detected and tested on the Marvell Armada A38x DB-88F6820-GP eval board.
So I take it you connected a memory oscilloscope to the i2c wires ?
No. I noticed that I2C doesn't work on this board with the current code. And checked for differences to the Linux code. And with this change, I2C does work on this board.
Ok (note neither have I measured the actual speed on Allwinner devices), lets wait a bit to see what Allwinner has to say.
Regards,
Hans
Hi,
On 17-03-15 12:15, Hans de Goede wrote:
Hi,
On 17-03-15 11:08, Stefan Roese wrote:
The current implementation for baudrate calculation is incorrect. This part from the formula:
"2 ^ (n + 1)" is not equivalent to (1 << n) but to (2 << n)!
This patch fixes this and moves this calculation to a function instead of using a macro.
Hmm, this does not match with what the Allwinner datasheets say: https://github.com/allwinner-zh/documents/blob/master/A20/A20%20user%20manua...
They say:
Fsamp = F 0 = Fin / 2^CLK_N F1 = F0 / (CLK_M + 1) Foscl = F1 / 10 = Fin / (2^CLK_N * (CLK_M + 1)*10)
With Foscl being the ultimate i2c speed. Notice that they are talking about 2 ^ CLK_N not 2 ^ (CLK_N + 1)
And they have a few examples which match this. Now it could be that a register value of 0 means CLK_N = 1, reg 1 CLK_N = 2, etc. this is not clearly specified ...
This new function is taken from the Linux kernel.
Interesting, because on Allwinnner / sunxi devices we are using the kernel driver formula unmodified, and things seem to work fine despite this. Could be tolerances allowing this, could be the Allwinner datasheet being unclear.
I've send allwinner a mail asking them to clarify this.
I've just gotten an answer from allwinner, and the formula in their datasheet is correct, with the raw register value == CLK_N so the current (before this patch) u-boot code is correct for Allwinner devices and we need a #ifdef here to keep the old formula for sunxi devices, you can use:
#ifdef CONFIG_SUNXI
For this.
Regards,
Hans
Hi,
On 18-03-15 09:20, Hans de Goede wrote:
Hi,
On 17-03-15 12:15, Hans de Goede wrote:
Hi,
On 17-03-15 11:08, Stefan Roese wrote:
The current implementation for baudrate calculation is incorrect. This part from the formula:
"2 ^ (n + 1)" is not equivalent to (1 << n) but to (2 << n)!
This patch fixes this and moves this calculation to a function instead of using a macro.
Hmm, this does not match with what the Allwinner datasheets say: https://github.com/allwinner-zh/documents/blob/master/A20/A20%20user%20manua...
They say:
Fsamp = F 0 = Fin / 2^CLK_N F1 = F0 / (CLK_M + 1) Foscl = F1 / 10 = Fin / (2^CLK_N * (CLK_M + 1)*10)
With Foscl being the ultimate i2c speed. Notice that they are talking about 2 ^ CLK_N not 2 ^ (CLK_N + 1)
And they have a few examples which match this. Now it could be that a register value of 0 means CLK_N = 1, reg 1 CLK_N = 2, etc. this is not clearly specified ...
This new function is taken from the Linux kernel.
Interesting, because on Allwinnner / sunxi devices we are using the kernel driver formula unmodified, and things seem to work fine despite this. Could be tolerances allowing this, could be the Allwinner datasheet being unclear.
I've send allwinner a mail asking them to clarify this.
I've just gotten an answer from allwinner, and the formula in their datasheet is correct, with the raw register value == CLK_N so the current (before this patch) u-boot code is correct for Allwinner devices and we need a #ifdef here to keep the old formula for sunxi devices, you can use:
p.s.
This means the kernel currently does the wrong thing on Allwinner, I've put fixing this on my todo list.
Regards,
Hans
Hi Hans,
On 18.03.2015 09:20, Hans de Goede wrote:
<snip>
I've send allwinner a mail asking them to clarify this.
I've just gotten an answer from allwinner, and the formula in their datasheet is correct, with the raw register value == CLK_N so the current (before this patch) u-boot code is correct for Allwinner devices and we need a #ifdef here to keep the old formula for sunxi devices, you can use:
#ifdef CONFIG_SUNXI
For this.
Okay, will send v2 right away...
Thanks, Stefan
participants (2)
-
Hans de Goede -
Stefan Roese