I've no idea how ioremap() works, never used it. But if it's similar to how mmap() works on /dev/mem/, it does not matter what state the hardware module is in. Of course there are a few specified steps one must do in order to get a device working if it's not already. But if the device is already on, and functional, you can essentially override that module with mmap() and /dev/mem/. But it's probably not good idea, as the kernel will still think it has control . . .
Anyway, I'm not sure I'd exactly call this a "driver" per se, as it's being done in userspace. But others might argue it's what's called a userspace driver . . . and yeah, I do not know about that. If you start changing pixels on your screen by poking at memory locations through /dev/mem/ does that mean you've created a graphics driver ? No . . . On Thu, Dec 17, 2015 at 4:08 PM, John Syne <[email protected]> wrote: > > On Dec 17, 2015, at 3:00 PM, William Hermans <[email protected]> wrote: > > *That is a good point. To understand how to enable the power and clock for >> McASP, look at the Starterware examples for McASP as they do everything you >> need to make this work.* >> > > Probably easier, and more productive to read the TRM for the AM335x > processors . . . All address offsets should be listed there as well, and > the introduction for hardware module will give a short explanation of what > needs doing, in order to bring the module up. > > Yeah, thinking about what Charles said, if he defines the McASP in the > device tree, it should setup everything he needs. One problem I’m not sure > how to overcome, he needs a device driver defined for the McASP or else the > clock and power won’t be setup. But if he has a device driver setup, then > it will conflict with his application. So that is why I think he has to do > all this manually. > > Regards, > John > > > On Thu, Dec 17, 2015 at 3:15 PM, John Syne <[email protected]> wrote: > >> >> >> > On Dec 17, 2015, at 1:59 PM, Charles Steinkuehler < >> [email protected]> wrote: >> > >> > On 12/17/2015 2:04 PM, [email protected] wrote: >> >> I am trying to access the McASP control registers. Reading from the >> first >> >> one fails with the kernel oops stating "external abort on >> non-linefetch >> >> (0x1028)". I dont know what that means. A minimum failing example of >> the >> >> code is below: >> > >> > <snip> >> > >> >> I have also tried request_mem_region around it, but that changes >> nothing. >> >> The sound drivers are not loaded, and the devicetree entry for the >> McASP is >> >> disabled, so there shouldn't be any problems with conflicts. >> > >> > One way to get this error is if the hardware you are talking to is >> > disabled. You need to either enable the hardware via the device tree, >> > or otherwise manage to setup the low-level SoC registers so the McASP >> > is provided a clock, power, and is taken out of reset. >> > >> > Most of the hardware blocks on the AM335x series can be individually >> > enabled or shut-down to save power. >> That is a good point. To understand how to enable the power and clock for >> McASP, look at the Starterware examples for McASP as they do everything you >> need to make this work. >> >> Regards, >> John >> > >> > -- >> > Charles Steinkuehler >> > [email protected] >> > >> > -- >> > For more options, visit http://beagleboard.org/discuss >> > --- >> > You received this message because you are subscribed to the Google >> Groups "BeagleBoard" group. >> > To unsubscribe from this group and stop receiving emails from it, send >> an email to [email protected]. >> > For more options, visit https://groups.google.com/d/optout. >> >> -- >> For more options, visit http://beagleboard.org/discuss >> --- >> You received this message because you are subscribed to the Google Groups >> "BeagleBoard" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> For more options, visit https://groups.google.com/d/optout. >> > > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. > > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
