On Sun, Sep 30, 2012 at 12:50 PM, Roland Stigge <sti...@antcom.de> wrote: > On 30/09/12 11:35, Stijn Devriendt wrote: >> In our kernel tree we have similar code. If you like I can request >> permission >> to share. I can, however, already give you an update on the basic >> structure, perhaps >> it's useful now. >> >> For the first part, the drivers need to implement a the gpio interface >> for groups. >> gpio_set_multi, gpio_get_multi, gpio_direction_input_multi, >> gpio_direction_output_multi. Each of them gets a 'u32 mask'. >> >> Secondly, gpiolib gets some new code to handle groups: >> groups are requested via a list of gpio ids. Mind that order is respected: >> request( [1, 5, 2, 4] ) followed by a set(0x5) will translate to >> gpio_set_multi( 0x18 ). An opaque gpio_group struct is used to keep track. >> This means the gpiolib interface also has a u32 mask, but translation is >> done for the gpio-drivers. >> >> There is some code to request groups via device-tree (again respecting >> order) >> and there are also platform driver structures. >> >> gpiolib was also extended to export groups into sysfs, respecting policy >> (input, output, user-selectable) and to make softlinks to groups in other >> driver's subdir. (One driver we use this in is a power-sequencer with 2 >> gpios selecting a margining profile, this driver then has the gpio_group >> exported in it's sysfs dir as .../profile, allowing H/W engineers to select >> the profile without voltage glitches) >> >> There's also a separate driver, that does nothing more than exporting >> both individual pins and groups to userspace based on platform description >> or devicetree. This is probably less interesting for mainline, since we're >> abusing device-tree to do away with some init script that can do the same. >> >> The rationale behind a 32bit mask is that typical processors can at most >> set one processor-word worth of GPIOs at once and there are probably >> few chips with over 32GPIOs on a single gpio_chip anyway. >> Nevertheless, in the era of 64bit, it's definitely possible to go for >> u64 instead. > > Hi Stijn, > > thank you for your notes! > > Besides what I discussed with JC and Linus, I find the unsigned int > (i.e. u32 or u64, depending on the arch) quite appealing. It is a nice > compromise between my general bit mapped data model (variable size *u8 > array) and the bool *values list. Even maps easily onto a single sysfs > entry for values, by abstracting a gpio list to an actual data word. > > What do others think? JC? Linus? I'm considering this (unsigned int > data) a valid option. > > One question: How did you solve the one-value-per-file in the sysfs > interface? > By exporting the group as a whole: /sys/.../gpiogroup248/value where value contains a decimal representing the group value. Again, this respects the ordering of the pins:
Actual pins: 0x2D (b 0010 1101) Selected pins: 6 3 0 1 Readout: 6 (b 0 1 1 0) The export sysfs file does, however, accept multiple gpio IDs for groups. Not sure if this is a 'violation' per se... If the user stores a single value he gets a single pin, multiple (space-separated) values give him a group. Regards, Stijn -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
