Date: Wed, 17 Mar 2010 08:40:57 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-arch@freebsd.org Cc: Cole <cole@opteqint.net> Subject: Re: PCI and Resouce question Message-ID: <201003170840.57911.jhb@freebsd.org> In-Reply-To: <9f206d1a1003170250r2727a55ajb636a0bdf1a2f137@mail.gmail.com> References: <9f206d1a1003170250r2727a55ajb636a0bdf1a2f137@mail.gmail.com>
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On Wednesday 17 March 2010 5:50:14 am Cole wrote: > Hi. > > Sorry if this is not the correct list, I have tried posting to > freebsd-hackers, and didnt get a response. Maybe im being stupid and > not connecting something, or just not understanding, in which case > sorry again. > > What im trying to achieve is writing to a few registers/memory > addresses for the memory location of BAR 0 for a pci card. I do not > want to modify the drivers source code, since it might become > unavailable sometime in the future. So what im looking to do is write > another kernel module, that can obtain the cards device_t structure, > as well as the resource structure of the card. My aim is to obtain the > resource structure so that I can then obtain the bus_tag and > bus_handle, and use those to write to the BAR 0 memory space. > > My understanding is that I would use pci_find_device to obtain the > device_t, then I think I can use bus_alloc_resource_any to obtain the > resource, I see there used to be a bus_get_resource, but the man page > for that no longer seems to exist, and references to it seem to have > been removed. If there is another way or better way of doing this, > please let me know. Also im not familiar with the specifics of > bus_alloc_resouce_any, and I dont know if calling this function from > another kernel module will give me the already allocated memory for > this pci card, or will it create a new one and assign it to the BAR 0 > register on the card? The PCI bus expects that only the driver calls bus_alloc_resource_any(), and that it only does this once. bus_get_resource() does not return the actual 'struct resource *r', so it will not do you any good. If you know for certain that the existing driver has not called 'bus_alloc_resource_any()', then you can call it from your module. Note that if the device driver is unloaded, the PCI bus may unmap the resource out from under your module (the PCI bus assumes that only the child device_t uses the resources, so it cleans up allocated resources when a driver unloads). Really, the clean way to handle something like this is to have your new code to share the device_t with the other driver. You can do this by using an approach similar to the vga_pci driver and changing the existing driver to attach to your device instead. So long as you propogate/emulate the proper PCI and bus methods, the child device driver can work fine with only a one- line change to add a new DRIVER_MODULE() that attaches to your device as the bus instead of pci. For, example, if your driver creates 'foo0' devices and the existing driver is called 'bar', you would create a new line: DRIVER_MODULE(bar, foo, ...); where the rest of the fields are copied from the existing 'DRIVER_MODULE(bar, pci)' line. Your foo driver will have to have a higher probe priority than the real driver, and you will have to load your driver before the real driver. Another alternative would be to make the real driver become the proxy driver. Attach your driver as a child of it. You will have to add bus and PCI methods to the real driver to satisfy the needs of your device. Mostly you just want this driver to have a custom methods for allocating resources where it shares a resource it has already allocated with your driver. -- John Baldwin
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