Messages in this thread | | | From | Grant Likely <> | Subject | Re: Device tree node to major/minor? | Date | Wed, 21 Nov 2012 15:47:58 +0000 |
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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.
g.
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