Re: [PATCH] i2c: Adding the i2c-bit-platform bus

[Eran Duchan <pavius-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Argh, the patch won't pass checkpatch because I brilliantly submitted
it via gmail. Once the 2 issues (initializing SDA/SCL and platform
structure) are discussed and agreed I'll resubmit the patch via git.

Thanks
Eran

On Sat, May 7, 2011 at 2:53 PM, Eran Duchan <pavius-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Hi guys,
>
> Following the discussion on the matter of i2c-gpio performance, I'm
> submitting this very simple patch which adds i2c-bit-platform. Using
> this driver, a platform can register callbacks called by i2c-bit-algo
> so that it can modify GPIO pins directly or do pretty much anything
> else. Besides style, I see 2 points for discussion:
>
> 1) Should the i2c-bit-platform call setscl/setsda passing state to 1
> (so that SDA/SCL are explicitly pulled high) on probe or should this
> be implemented in the platforms which mandate this? In the patch I
> left it up to the platform.
>
> 2) Which platform_data structure is passed to the driver? There are
> three options:
> 2.a) Currently in the patch - just expect a i2c_algo_bit_data
> structure. No new structures introduced, but this does expose some
> underlying bit-algo detail to the platform and does not elegantly
> support passing any future i2c-bit-platform specific fields, should
> they be required.
> 2.b) Declare a new platform structure which has a i2c_algo_bit_data
> member (for supporting future i2c-bit-platform fields). Solves the
> future field issue but still exposes so bit-algo stuff to the platform
> 2.c) Declare a new platform structure with members similar to
> i2c_algo_bit_data, but only those who should be exposed to the
> platform. The only downside to this is that any future change to
> i2c_algo_bit_data may require change to this new platform structure.
>
> Tested on an MPC875 running @ 50MHz to achieve near perfect 100kHz I2C.
>
> Eran
>
> Signed-off-by: Eran Duchan <pavius-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
>  drivers/i2c/busses/Kconfig            |   10 +++
>  drivers/i2c/busses/Makefile           |    1 +
>  drivers/i2c/busses/i2c-bit-platform.c |  105 +++++++++++++++++++++++++++++++++
>  3 files changed, 116 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/i2c/busses/i2c-bit-platform.c
>
> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index 3a6321c..f6c6b8c 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -365,6 +365,16 @@ config I2C_GPIO
>          This is a very simple bitbanging I2C driver utilizing the
>          arch-neutral GPIO API to control the SCL and SDA lines.
>
> +config I2C_BIT_PLATFORM
> +       tristate "I2c-bit-algo as platform device"
> +       select I2C_ALGOBIT
> +       help
> +         An I2C bus adapter which delegates the bit-algo callback registration
> +         to the platform. Useful in cases where existing adapters such as
> +         i2c-gpio are too slow. Keep in mind that no resource locking of any kind
> +         is performed by the adapter or algo, so any such contention must be
> +         handled by the platform.
> +
>  config I2C_HIGHLANDER
>        tristate "Highlander FPGA SMBus interface"
>        depends on SH_HIGHLANDER
> diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
> index 84cb16a..65bced4 100644
> --- a/drivers/i2c/busses/Makefile
> +++ b/drivers/i2c/busses/Makefile
> @@ -35,6 +35,7 @@ obj-$(CONFIG_I2C_CPM)         += i2c-cpm.o
>  obj-$(CONFIG_I2C_DAVINCI)      += i2c-davinci.o
>  obj-$(CONFIG_I2C_DESIGNWARE)   += i2c-designware.o
>  obj-$(CONFIG_I2C_GPIO)         += i2c-gpio.o
> +obj-$(CONFIG_I2C_BIT_PLATFORM) += i2c-bit-platform.o
>  obj-$(CONFIG_I2C_HIGHLANDER)   += i2c-highlander.o
>  obj-$(CONFIG_I2C_IBM_IIC)      += i2c-ibm_iic.o
>  obj-$(CONFIG_I2C_IMX)          += i2c-imx.o
> diff --git a/drivers/i2c/busses/i2c-bit-platform.c
> b/drivers/i2c/busses/i2c-bit-platform.c
> new file mode 100644
> index 0000000..cb98006
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-bit-platform.c
> @@ -0,0 +1,105 @@
> +/*
> +    i2c-bit-algo as platform device
> +    Delegates the bit-algo callback registration to the platform
> +
> +    Copyright (C) 2011 Eran Duchan <pavius-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> +
> +    This program is free software; you can redistribute it and/or modify
> +    it under the terms of the GNU General Public License as published by
> +    the Free Software Foundation; either version 2 of the License, or
> +    (at your option) any later version.
> +*/
> +
> +#include <linux/i2c.h>
> +#include <linux/i2c-algo-bit.h>
> +#include <linux/slab.h>
> +
> +static int __devinit i2c_bit_platform_probe(struct platform_device *pdev)
> +{
> +       struct i2c_algo_bit_data *bit_data;
> +       struct i2c_adapter *adap;
> +       int ret;
> +
> +       if (pdev->dev.platform_data == NULL)
> +               ret = -ENXIO;
> +
> +       bit_data = pdev->dev.platform_data;
> +
> +       ret = -ENOMEM;
> +       adap = kzalloc(sizeof(struct i2c_adapter), GFP_KERNEL);
> +       if (adap == NULL)
> +               goto err_alloc_adap;
> +
> +       adap->owner = THIS_MODULE;
> +       adap->algo_data = bit_data;
> +       adap->class = I2C_CLASS_HWMON | I2C_CLASS_SPD;
> +       adap->dev.parent = &pdev->dev;
> +
> +       snprintf(adap->name, sizeof(adap->name), "i2c-bit-platform%d",
> +                        pdev->id);
> +       adap->name[sizeof(adap->name) - 1] = '\0';
> +
> +       /*
> +        * If "dev->id" is negative we consider it as zero.
> +        * The reason to do so is to avoid sysfs names that only make
> +        * sense when there are multiple adapters.
> +        */
> +       adap->nr = (pdev->id != -1) ? pdev->id : 0;
> +       ret = i2c_bit_add_numbered_bus(adap);
> +       if (ret)
> +               goto err_add_bus;
> +
> +       platform_set_drvdata(pdev, adap);
> +
> +       return 0;
> +
> +err_add_bus:
> +err_alloc_adap:
> +
> +       kfree(adap);
> +
> +       return ret;
> +}
> +
> +static int __devexit i2c_bit_platform_remove(struct platform_device *pdev)
> +{
> +       struct i2c_adapter *adap;
> +
> +       adap = platform_get_drvdata(pdev);
> +
> +       i2c_del_adapter(adap);
> +       kfree(adap);
> +
> +       return 0;
> +}
> +
> +static struct platform_driver i2c_bit_platform_driver = {
> +       .driver         = {
> +               .name   = "i2c-bit-platform",
> +               .owner  = THIS_MODULE,
> +       },
> +       .probe          = i2c_bit_platform_probe,
> +       .remove         = __devexit_p(i2c_bit_platform_remove),
> +};
> +
> +static int __init i2c_bit_platform_init(void)
> +{
> +       int ret;
> +
> +       ret = platform_driver_register(&i2c_bit_platform_driver);
> +       if (ret)
> +               printk(KERN_ERR "i2c-bit-platform: probe failed: %d\n", ret);
> +
> +       return ret;
> +}
> +subsys_initcall(i2c_bit_platform_init);
> +
> +static void __exit i2c_bit_platform_exit(void)
> +{
> +       platform_driver_unregister(&i2c_bit_platform_driver);
> +}
> +module_exit(i2c_bit_platform_exit);
> +
> +MODULE_AUTHOR("Eran Duchan <pavius-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>");
> +MODULE_DESCRIPTION("Thin platform adapter for i2c-bit-algo");
> +MODULE_LICENSE("GPL");
> --
> 1.7.0.4
>