Messages in this thread | | | Date | Wed, 21 Nov 2012 12:48:09 -0800 | Subject | Re: Device tree node to major/minor? | From | Simon Glass <> |
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Hi Grant,
On Wed, Nov 21, 2012 at 7:47 AM, Grant Likely <grant.likely@secretlab.ca> wrote: > On Tue, 20 Nov 2012 15:48:24 -0800, Simon Glass <sjg@chromium.org> wrote: >> Hi Grant, >> >> On Tue, Nov 20, 2012 at 2:32 PM, Grant Likely <grant.likely@secretlab.ca> wrote: >> > On Tue, Nov 20, 2012 at 10:23 PM, Simon Glass <sjg@chromium.org> wrote: >> >> Hi, >> >> >> >> I hope this is a stupid question with an easy answer, but I cannot find it. >> >> >> >> I have a device tree node for an mmc block device and I want to use >> >> that block device from another driver. I have a phandle which lets me >> >> get the node of the mmc device, but I am not sure how to convert that >> >> into a block_device. In order to do so, I think I need a major/minor >> >> number. Of course the phandle might in fact point to a SCSI driver and >> >> I want that to work correctly also. >> >> >> >> I imagine I might be able to search through the wonders of sysfs in >> >> user space, but is there a better way? >> > >> > Do you /want/ to do it from userspace? What is your use case? Mounting >> > the rootfs? >> >> The use case is storing some raw data on a block device from within a >> driver in the kernel. It is used to keep track of the verified boot >> state. >> >> > >> > Regardless, userspace can monitor the uevents when devices are added >> > (that's what udev does) and watch for the full path of the node you >> > want in the uevent attribute. Then you can look for the child device >> > with the block major/minor numbers in it. >> >> So is there a way to do this entirely in the kernel ex post? It might >> need to happen during kernel boot, before user space. > > Yes, it is certainly doable within the kernel. First, you'll need to use > a notifier to get called back whenever a new device is created. Then > you'll need to look at the dev->of_node(->full_name) to see if it is the > node you actually want. You might need/want to resolve it from an alias > or something, but I presume you already have a way to find the > device_node before seaching for a struct device.
OK thank you. Was hoping to find a simple way to find a block device from a device tree node (yes I know the right one) but I suppose in general this is impossible, since nodes may create more than one device, and each has its own data structures leading to the block device.
So it seems like a notifier is the best way. Thanks for looking at this Grant.
Regards, Simon
> > g.
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