On Wed, 25 Nov 2020 at 16:49, Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx> wrote: > > On 11/25/2020 8:42 AM, Jeffrey Hugo wrote: > > On 11/25/2020 8:43 AM, Loic Poulain wrote: > >> Today the MHI controller name is simply cloned from the underlying > >> bus device (its parent), that gives the following device structure > >> for e.g. a MHI/PCI controller: > >> devices/pci0000:00/0000:00:01.2/0000:02:00.0/0000:02:00.0 > >> devices/pci0000:00/0000:00:01.2/0000:02:00.0/0000:02:00.0/0000:02:00.0_IPCR > >> > >> ... > >> > >> That's quite misleading/confusing and can cause device registering > >> issues because of duplicate dev name (e.g. if a PCI device register > >> two different MHI instances). > >> > >> This patch changes MHI core to create indexed mhi controller names > >> (mhi0, mhi1...) in the same way as other busses (i2c0, usb0...). > >> > >> The previous example becomes: > >> devices/pci0000:00/0000:00:01.2/0000:02:00.0/mhi0 > >> devices/pci0000:00/0000:00:01.2/0000:02:00.0/mhi0/mhi0_IPCR > >> ... > >> > >> Signed-off-by: Loic Poulain <loic.poulain@xxxxxxxxxx> > > > > > > How does this change /sys/bus/mhi/devices/ ? > > > > The point of having the bus name in the mhi device name is to give an > > easy way to correlate those devices back to the "root" device (I have a > > lot of users which do that). > > > > Also, do we actually have some device that actually exposes multiple MHI > > interfaces? > > > > > > Looking at the code change itself, looks like the controller index is > essentially random, and not persistent. Is that expected? > > I'm thinking it might be confusing if you have say 12 MHI controllers > from 12 different devices, and some of those devices crash at roughly > the same time. The controllers get removed, and re-initialized, which > means that you have essentially a race condition where the controller > for the same device now has a different index. There is no race since ID is atomically allocated, but yes your controller can get a different index on unregister/register, like e.g network interfaces index, usb devices ID, video devices, etc... can be enumerated in various order. Not sure why the user should take care of the MHI controller index. > > -- > Jeffrey Hugo > Qualcomm Technologies, Inc. is a member of the > Code Aurora Forum, a Linux Foundation Collaborative Project.
