[lkml]   [2007]   [Nov]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [patch/rfc 2/4] pcf875x I2C GPIO expander driver
    On Friday 30 November 2007, Jean Delvare wrote:
    > So the user-space interface would be part of the generic GPIO
    > infrastructure? I like the idea.

    I thought that would make sense too! :) Someone would need to
    write the code though. Having such a mechanism would provide
    another "carrot" to migrate folk towards the gpiolib core.

    I think adding a gpiochip primitive to mark a (potential) GPIO
    as invalid would support the converse of /sys/kernel/debug/gpio.
    Invalid GPIOs include pins set up for non-GPIO usage (like being
    used for MMC or MII), or not wired up on a given board. Pins
    that were valid as GPIOs and not requested by a kernel driver
    might reasonably be managed by userspace code.

    > > > > +#include <linux/pcf857x.h>
    > > >
    > > > I suspect that there will be many more such header files in the future.
    > > > Would it make sense to move them to include/linux/gpio?
    > >
    > > I was thinking more like <linux/i2c/...> myself. There are many more
    > > I2C chips than GPIO expanders.
    > But most i2c chip drivers don't need a header file. Or is this going to
    > change with the new-style i2c drivers?

    I expect it will become a lot more common. Remember that legacy
    I2C drivers *couldn't* get any board-specific config data; that's
    been problematic, since it meant the drivers themselves ended up
    with lots of board-specific cruft. That prevented many drivers
    from going upstream at all. (As I mentioned about pcf8574 code,
    although in that case the problem was worsened by lack of any
    reusable kernel interface for such GPIO signals.)

    > Along the same line, I am wondering if it would make sense to put the
    > various GPIO drivers in drivers/gpio.

    Could be. Right now we have three "GPIO expander" drivers using
    the new "gpiolib" framework: pcf875x and pca9539 for I2C, and
    mcp23s08 for SPI. There are many more that *could* be used with
    Linux boxes. And there are other drivers/XYZ directories that
    are (currently) that small. Maybe gpiolib should go upstream
    like that, and lib/gpiolib should be in drivers/gpio too...

    However, keep in mind that lots of chips export a few GPIOs but
    don't have that as their core functionality ... one example is
    the drivers/i2c/chips/tps65010 driver. So it'd never be the
    case that GPIO drivers only live in that directory.

    - Dave
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2007-11-30 22:01    [W:0.022 / U:52.932 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site