From: Marc Zyngier <firstname.lastname@example.org> To: Johan Hovold <email@example.com> Cc: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, Linus Walleij <email@example.com>, Bartosz Golaszewski <firstname.lastname@example.org>, Greg Kroah-Hartman <email@example.com>, firstname.lastname@example.org Subject: Re: [PATCH 0/4] USB: ftdio_sio: GPIO validity fixes Date: Mon, 07 Dec 2020 14:41:03 +0000 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <X841xwCChUEqi5Ad@localhost> On 2020-12-07 14:01, Johan Hovold wrote: > On Fri, Dec 04, 2020 at 04:47:35PM +0000, Marc Zyngier wrote: >> Having recently tried to use the CBUS GPIOs that come thanks to the >> ftdio_sio driver, it occurred to me that the driver has a couple of >> usability issues: >> >> - it advertises potential GPIOs that are reserved to other uses (LED >> control, or something else) > > Consider the alternative, that the gpio offsets (for CBUS0, CBUS1, > CBUS2 > or CBUS4) varies depending on how the pins have been muxed. Hardly very > user friendly. That's not what I suggest. If you want fixed GPIO offsets, fine by me. But telling the user "these are GPIOs you can use", and then "on second though, you can't" is not exactly consistent. >> - it returns an odd error (-ENODEV), instead of the expected -EINVAL >> when a line is unavailable, leading to a difficult diagnostic > > Hmm, maybe. Several gpio driver return -ENODEV when trying to request > reserved pins. Even gpiolib returns -ENODEV when a pins is not yet > available due to probe deferal. -ENODEV really means "no GPIOchip" in this context. The fact that other drivers return -ENODEV for reserved pins looks like a bug to me. > -EBUSY could also be an alternative, but that's used to indicate that a > line is already in use as a gpio. Or something else. Which is exactly the case, as it's been allocated to another function. >> We address the issues in a number of ways: >> >> - Stop reporting invalid GPIO lines as valid to userspace. It >> definitely seems odd to do so. Instead, report the line as being >> used, making the userspace interface a bit more consistent. >> >> - Implement the init_valid_mask() callback in the ftdi_sio driver, >> allowing it to report which lines are actually valid. >> >> - As suggested by Linus, give an indication to the user of why some of >> the GPIO lines are unavailable, and point them to a useful tool >> (once per boot). It is a bit sad that there next to no documentation >> on how to use these CBUS pins. > > Don't be sad, Marc; write some documentation. ;) I sure will, right after I have fixed the rest of the kernel bugs I have introduced. With a bit of luck, that's right after I finally kick the bucket. M. -- Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2020-12-07 14:42 UTC|newest] Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-04 16:47 Marc Zyngier 2020-12-04 16:47 ` [PATCH 1/4] gpiolib: cdev: Flag invalid GPIOs as used Marc Zyngier 2020-12-07 14:16 ` Johan Hovold 2020-12-07 14:59 ` Marc Zyngier 2020-12-09 9:25 ` Linus Walleij 2020-12-04 16:47 ` [PATCH 2/4] USB: serial: ftdi_sio: Report the valid GPIO lines to gpiolib Marc Zyngier 2020-12-09 9:28 ` Linus Walleij 2020-12-04 16:47 ` [PATCH 3/4] USB: serial: ftdi_sio: Log the CBUS GPIO validity Marc Zyngier 2020-12-07 14:29 ` Johan Hovold 2020-12-07 15:00 ` Marc Zyngier 2020-12-07 15:19 ` Johan Hovold 2020-12-09 9:35 ` Linus Walleij 2020-12-09 17:05 ` Johan Hovold 2020-12-09 17:39 ` Johan Hovold 2020-12-04 16:47 ` [PATCH 4/4] USB: serial: ftdi_sio: Drop GPIO line checking dead code Marc Zyngier 2020-12-07 9:55 ` [PATCH 0/4] USB: ftdio_sio: GPIO validity fixes Andy Shevchenko 2020-12-07 14:01 ` Johan Hovold 2020-12-07 14:41 ` Marc Zyngier [this message] 2020-12-07 15:08 ` Johan Hovold 2020-12-07 15:34 ` Marc Zyngier 2020-12-07 15:49 ` Johan Hovold 2020-12-09 9:20 ` Linus Walleij 2020-12-09 15:42 ` Johan Hovold
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