Date: Wed, 17 Mar 2010 20:18:30 +0200 From: Cole <cole@opteqint.net> To: freebsd-arch@freebsd.org Subject: Re: PCI and Resouce question Message-ID: <9f206d1a1003171118x6bf16f9crba0063c550c3b007@mail.gmail.com> In-Reply-To: <201003170840.57911.jhb@freebsd.org> References: <9f206d1a1003170250r2727a55ajb636a0bdf1a2f137@mail.gmail.com> <201003170840.57911.jhb@freebsd.org>
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Hi. Thanks for explaining it and making it clearer, and thanks to everyone who commented. It makes things a lot easier to understand I know now how to sort this out. Thanks again /Cole On 17 March 2010 14:40, John Baldwin <jhb@freebsd.org> wrote: > 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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