Hi Doug, On Tue, Oct 22, 2024 at 2:28 AM Doug Anderson <dianders@xxxxxxxxxxxx> wrote: > On Mon, Oct 21, 2024 at 1:48 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > On Mon, Oct 21, 2024 at 10:23 AM Geert Uytterhoeven > > <geert@xxxxxxxxxxxxxx> wrote: > > > On Mon, Oct 21, 2024 at 9:27 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Mon, Oct 21, 2024 at 08:58:30AM +0200, Geert Uytterhoeven wrote: > > > > > On Mon, Oct 21, 2024 at 8:39 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Sun, Oct 20, 2024 at 05:36:29PM +0300, Laurent Pinchart wrote: > > > > > > > On Fri, Oct 18, 2024 at 04:31:21PM +0200, Greg KH wrote: > > > > > > > > On Fri, Oct 18, 2024 at 05:25:22PM +0300, Laurent Pinchart wrote: > > > > > > > > > On Fri, Oct 18, 2024 at 04:09:26PM +0200, Greg KH wrote: > > > > > > > > > > On Fri, Oct 18, 2024 at 03:36:48PM +0200, Geert Uytterhoeven wrote: > > > > > > > > > > > On Fri, Oct 18, 2024 at 3:10 PM Laurent Pinchart wrote: > > > > > > > > > > > > On Fri, Oct 18, 2024 at 09:45:52AM +0200, Geert Uytterhoeven wrote: > > > > > > > > > > > > > Each bridge instance creates up to four auxiliary devices with different > > > > > > > > > > > > > names. However, their IDs are always zero, causing duplicate filename > > > > > > > > > > > > > errors when a system has multiple bridges: > > > > > > > > > > > > > > > > > > > > > > > > > > sysfs: cannot create duplicate filename '/bus/auxiliary/devices/ti_sn65dsi86.gpio.0' > > > > > > > > > > > > > > > > > > > > > > > > > > Fix this by using a unique instance ID per bridge instance. > > > > > > > > > > > > > > > > > > > > > > > > Isn't this something that should be handled by the AUX core ? The code > > > > > > > > > > > > below would otherwise need to be duplicated by all drivers, which seems > > > > > > > > > > > > a burden we should avoid. > > > > > > > > > > > > > > > > > > > > > > According to the documentation, this is the responsibility of the caller > > > > > > > > > > > https://elixir.bootlin.com/linux/v6.11.4/source/include/linux/auxiliary_bus.h#L81 > > > > > > > > > > > I believe this is the same for platform devices. > > > > > > > > > > > See also the example at > > > > > > > > > > > https://elixir.bootlin.com/linux/v6.11.4/source/include/linux/auxiliary_bus.h#L116 > > > > > > > > > > > > > > > > > > > > > > Note: the platform bus supports PLATFORM_DEVID_AUTO, but the auxiliary > > > > > > > > > > > bus does not. > > > > > > > > > > > > > > > > > > > > Yes, it does not as it's up to the caller to create a unique name, like > > > > > > > > > > your patch here does. I'd argue that platform should also not do > > > > > > > > > > automatic device ids, but that's a different argument :) > > > > > > > > > > > > > > > > > > __auxiliary_device_add() creates the device name with > > > > > > > > > > > > > > > > > > dev_set_name(dev, "%s.%s.%d", modname, auxdev->name, auxdev->id); > > > > > > > > > > > > > > > > > > I'm not calling for a PLATFORM_DEVID_AUTO-like feature here, but > > > > > > > > > shouldn't the first component of the device name use the parent's name > > > > > > > > > instead of the module name ? > > > > > > > > > > > > > > > > Why would the parent's name not be the module name? That name is > > > > > > > > guaranteed unique in the system. If you want "uniqueness" within the > > > > > > > > driver/module, use the name and id field please. > > > > > > > > > > > > > > > > That's worked well so far, but to be fair, aux devices are pretty new. > > > > > > > > What problem is this naming scheme causing? > > > > > > > > > > > > > > Auxiliary devices are created as children of a parent device. When > > > > > > > multiple instances of the same parent type exist, this will be reflected > > > > > > > in the /sys/devices/ devices tree hierarchy without any issue. The > > > > > > > problem comes from the fact the the auxiliary devices need a unique name > > > > > > > for /sys/bus/auxialiary/devices/, where we somehow have to differenciate > > > > > > > devices of identical types. > > > > > > > > > > > > > > Essentially, we're trying to summarize a whole hierarchy (path in > > > > > > > /sys/devices/) into a single string. There are different ways to solve > > > > > > > this. For platform devices, we use a device ID. For I2C devices, we use > > > > > > > the parent's bus number. Other buses use different schemes. > > > > > > > > > > > > > > Geert's patch implements a mechanism in the ti-sn65dsi86 driver to > > > > > > > handle this, and assign an id managed by the parent. In a sense we could > > > > > > > consider this to be similar to what is done for I2C, where the bus > > > > > > > number is also a property of the parent. However, the big difference is > > > > > > > that the I2C bus number is managed by the I2C subsystem, while here the > > > > > > > id is managed by the ti-sn65dsi86 driver, not by the auxiliary device > > > > > > > core. This would require duplicating the same mechanism in every single > > > > > > > driver creating auxiliary devices. This strikes me as a fairly bad idea. > > > > > > > The problem should be solved by the core, not by individual drivers. > > > > > > > > > > > > The "id" is just a unique number, it is "managed" by the thing that is > > > > > > creating the devices themselves, not the aux core code. I don't see why > > > > > > the i2c bus number has to match the same number that the ti driver > > > > > > creates, it could be anything, as long as it doesn't match anything else > > > > > > currently created by that driver. > > > > > > > > > > Laurent does not say it has to match the i2c bus number. > > > > > He does think the auxilliary bus should provide a mechanism to > > > > > allocate these IDs (e.g. usin g AUX_DEVID_AUTO?). > > > > > > > > As this is the first subsystem to ask for such a thing, I didn't think > > > > it was needed, but the aux subsystem is new :) > > > > > > > > > However, using i2c_client->adapter->nr instead of ida_alloc() > > > > > in the TI driver does sound like a good idea to me... > > > > > > > > Great! > > > > > With the I2C adapter numbers, that becomes: > > > > > > /sys/bus/auxiliary/devices > > > ├── ti_sn65dsi86.gpio.1 > > > ├── ti_sn65dsi86.pwm.1 > > > ├── ti_sn65dsi86.aux.1 > > > ├── ti_sn65dsi86.bridge.1 > > > ├── ti_sn65dsi86.gpio.4 > > > ├── ti_sn65dsi86.pwm.4 > > > ├── ti_sn65dsi86.aux.4 > > > └── ti_sn65dsi86.bridge.4 > > > > > > > adapter->nr instead like other aux subsystems already do. > > > > Unfortunately the devil is in the details, as usual: there can be > > multiple instances of the sn65dsi86 bridge on a single I2C bus, > > so adapter->nr is not guaranteed to generate a unique name. > > In the case of sn65dsi86 I think we'd actually be OK. The TI bridge > chip is always at bus address 0x2d so you can't have more than one on > the same bus. Unless you added something funky atop it (like a mux of > some sort) you might be OK. It's 0x2c on mine ;-) 8.5.1 Local I2C Interface Overview The 7-bit device address for SN65DSI86 is factory preset to 010110X with the least significant bit being determined by the ADDR control input. > > Changing the auxiliary bus to use the parent's name instead of the > > module name, as suggested by Laurent, would fix that. > > Right. On my system dev_name() of the sn65dsi86 device is "2-002d". If > we had a second on i2c bus 4, we'd have: > > /sys/bus/auxiliary/devices > ├── 2-002d.gpio.0 > ├── 2-002d.pwm.0 > ├── 2-002d.aux.0 > ├── 2-002d.bridge.0 > ├── 4-002d.gpio.0 > ├── 4-002d.pwm.0 > ├── 4-002d.aux.0 > └── 4-002d.bridge.0 > > ...and I think that's guaranteed to be unique because all the i2c > devices are flat in "/sys/bus/i2c/devices". Correct. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
