Le Fri, 7 Dec 2007 14:04:16 +0530, "Rajat Jain" <Rajat.Jain@xxxxxxxxxxxx> a écrit : > You need request_mem_region(). I'm not sure it's enough in Gavin's case. >From what I understand, request_mem_region() simply allows to reserve a memory region, to say « I'm using it », so that nobody else will use it. However, it doesn't do anything with regard to mapping this physical memory region in the virtual address space. After a quick look at several drivers using request_mem_region(), I have the impression that: * drivers handling peripherals that are driven through registers at a physical position already accessible through the kernel identity mapping only use request_mem_region() Ex: http://lxr.free-electrons.com/source/drivers/char/rtc.c#971 * drivers handling peripherals that are driven through registers at a physical position not accessible through the kernel identify mapping use both request_mem_region() and ioremap(). Ex: http://lxr.free-electrons.com/source/drivers/net/defxx.c#551 This is also confirmed by chapter 9 of Linux Device Drivers (http://lwn.net/images/pdf/LDD3/ch09.pdf), which says: « Allocation of I/O memory is not the only required step before that memory may be accessed. You must also ensure that this I/O memory has been made accessible to the kernel. Getting at I/O memory is not just a matter of dereferencing a pointer; on many systems, I/O memory is not directly accessible in this way at all. So a mapping must be set up first. This is the role of the ioremap function, introduced in the section “vmalloc and Friends” in Chapter 1. The function is designed specifically to assign virtual addresses to I/O memory regions. » Sincerly, Thomas -- Thomas Petazzoni, thomas.petazzoni@xxxxxxxx, http://thomas.enix.org Jabber, thomas.petazzoni@xxxxxxxxx Toulibre, http://www.toulibre.org - APRIL, http://www.april.org Fingerprint : 0BE1 4CF3 CEA4 AC9D CC6E 1624 F653 CB30 98D3 F7A7 -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
