Messages in this thread | | | Date | Mon, 12 Mar 2007 15:11:03 +0100 | From | Haavard Skinnemoen <> | Subject | Re: [PATCH v2] Bitbanging i2c bus driver using the GPIO API |
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On Sat, 10 Mar 2007 21:15:50 +0100 Jean Delvare <khali@linux-fr.org> wrote:
> I like the idea very much. Would this let us get rid of i2c-ixp2000? > i2c-ixp4xx? scx200_i2c? Other drivers?
Any platform that implements the generic gpio api should be able to use this driver. So yes, I hope we might be able to get rid of a few existing bitbanging drivers.
> > +/* > > + * Bitbanging i2c bus driver using the GPIO API > > + * > > + * Copyright (C) 2006 Atmel Corporation > > I'm told we're in year 2007 ;)
I'm also told that copyright protection lasts infinitely long in practice ;)
I'll update it. I probably just copied it blindly from a different driver.
> > +int i2c_gpio_getsda(void *data) > > +{ > > + struct i2c_gpio_platform_data *pdata = data; > > + > > + return gpio_get_value(pdata->sda_pin); > > +} > > > What value will you get if the SDA pin is open-drain and currently in > output mode? Are such GPIO pins actually able to detect that the pin is > low while they are not themselves driving it low?
I guess that depends on the GPIO controller. But being able to read the pin state even when the pin is configured as an output is a prerequisite for using this driver with "open drain" pins, so if the hardware doesn't support this, the board code should just set {sda,scl}_is_opendrain to zero.
> > + bit_data->udelay = 5, /* 100 kHz */ > > Actually, no, i2c-algo-bit has a 1/3-2/3 duty cycle, so a complete > cycle is 3 times the udelay value. So udelay=5 gives you 66 kHz. If > someone wants to fix that...
Ok. I guess we should move this parameter into the platform data struct anyway.
> Also, I wouldn't recommend such a low value when SCL cannot be sensed, > if a slave stretches the line even very briefly, you won't notice and > havoc will ensue. udelay=50 sounds more reasonable for such half-baked > busses.
Makes sense.
> > + ret = platform_driver_probe(&i2c_gpio_driver, i2c_gpio_probe); > > + if (ret) > > + printk("i2c-gpio: probe failed: %d\n", ret); > > Add KERN_ERR or similar.
Will do.
> Would you mind also adding yourself to MAINTAINERS for this driver? I > would appreciate it.
Sure. I'm hoping this driver won't cause that much maintenance overhead anyway since all the complicated stuff is in i2c-algo-bit. But I agree it needs a maintainer.
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