On Wed, Jan 10, 2024 at 1:40 PM Phil Howard <phil@xxxxxxxxxxxxx> wrote: > On Tue, 9 Jan 2024 at 14:00, Kent Gibson <warthog618@xxxxxxxxx> wrote: ... > > + Read Documentation/driver-api/gpio/drivers-on-gpio.rst to avoid reinventing > > + kernel wheels in userspace. > > I realise this is in part an emotional response, but very much > "citation needed" on > this one. While I believe Kernel drivers for things are a good idea, I > don't believe > userspace libraries are necessarily bad or wrong. They might be the first > experience a future kernel dev has with hardware. Either way there are multiple > ecosystems of userspace drivers both existing and thriving right now, and there > are good reasons to reinvent kernel wheels in userspace. > > At least some of these reasons relate to the (incorrectly assumed) > insurmountable > nature of kernel development vs just throwing together some Python. Including > this loaded language just serves to reinforce that. > > You catch more flies with honey than with vinegar, so I'd probably soften to: > > Before abusing userspace APIs to bitbash drivers for your hardware you should > read Documentation/driver-api/gpio/drivers-on-gpio.rst to see if your device has > an existing kernel driver. If not, please consider contributing one. I believe this note was motivated by the quite popular pyGPIO for RPi and MRAA for some platforms, which are the examples of how _not_ do things. ... > > +Each chip supports a number of GPIO lines, > > +:c:type:`chip.lines<gpiochip_info>`. Lines on the chip are identified by an > > +``offset`` in the range from 0 to ``chip.lines - 1``, i.e. `[0,chip.lines)`. > > I don't recognise this syntax "`[0,chip.lines)`", typo, or me being clueless? It's called "open interval", a mathematical term. ... > > + - - ``EFAULT`` Wondering if these constants can be referenced via % and if it makes sense. ... > > +The size of the kernel event buffer is fixed at the time of line request > > +creation, and can be influenced by the > > +:c:type:`request.event_buffer_size<gpio_v2_line_request>`. > > +The default size is 16 times the number of lines requested. > > This might explain why I could never quite get high-speed pulse counting to feel > right. Thank you! GPIO is just not a good tool for this kind of measurement. -- With Best Regards, Andy Shevchenko
