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    SubjectRe: [PATCH v2] Add GPIO-based MMC/SD driver
    On Sat, Jul 19, 2008 at 12:38:07AM +0200, Michael Buesch wrote:
    > Thanks for the comments.
    >
    > On Saturday 19 July 2008 00:10:37 Randy Dunlap wrote:
    > > > +To add a new device, simply echo the configuration string to the "add" file.
    > > > +The config string is composed out of the following elements:
    > > > +
    > > > +DEVNAME DIpin DOpin CLKpin CSpin SPIMODE MAXBUSSPEED NO_SPI_DELAY CSACTIVELOW
    > > > +
    > > > +DEVNAME is a unique name string for the device.
    > > > +DIpin is the SPI DI GPIO pin.
    > > > +DOpin is the SPI DO GPIO pin.
    > > > +CLKpin is the SPI CLOCK GPIO pin.
    > > > +CSpin is the SPI CHIPSELECT GPIO pin.
    > > > +SPIMODE is the hardware mode the device will run at. Can be 0-3.
    > > > +MAXBUSSPEED is the maximum bus speed in Hertz.
    > > > +NO_SPI_DELAY can be 1 or 0. If it is 1, then the lowlevel SPI delay
    > > > +will not be performed. This is not standards compliant, but may be required
    > > > +to gain reasonable speeds on embedded hardware.
    > > > +CSACTIVELOW can be 1 or 0. If it is 1, the chip is considered to be selected, if CS
    > > > +is at a logical 0.
    > > > +
    > >
    > > Would this be better done via configfs? sysfs files are supposed to be
    > > single-value files.
    >
    >
    > Well, I really want to avoid over-engineering this thing.
    > I thought about using configfs, but that would require to keep lots of state
    > information across the operations.
    > So one would have to allocate a device with mkdir. Then configure the parameters.
    > And then somehow tell the kernel to register it. State has to be maintained over
    > this time and I'm not sure how that "register" operation would look like.
    > Writing a "1" to a "register" file? So why not write all config parameters
    > to an "add" file and be done with all the stuff. ;)
    >
    > It all depends on how you define "one thing per file", IMO.
    > This "add" file does one thing. It creates a device. We must, of course, pass
    > some configuration parameters, too.

    We have precidence with this for the device id being "added" to a driver
    at run time in PCI and USB. Not that I really like this, I do think
    configfs would be better to do this with here instead of sysfs.

    That being said, as this is a new sysfs file, please break this
    documentation up into a file in the Documentation/ABI directory instead
    of here.

    thanks,

    greg k-h


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