[U-Boot] Peripheral multiplexing in devices

[U-Boot] Peripheral multiplexing in devices

[Vipin KUMAR]

Hi All,

This is with regards to the pad multiplexing in devices.

SPEAr SoCs support pin multiplexing(in hardware) to support multiple
peripherals by selecting a particular mode from a list of ten modes and
then selecting one of the two peripherals which can both be supported in
that mode. 
I hope I am clear :)

Now, we want to support this in sw in such a way that we have a single
image for linux for all possible configurations. We intend to do this
though bootloader (u-boot in this case)

SPEAr has an arm platform and linux-arm doesn't seem to support peripheral
multiplexing in the way we want. Though, I could see some stuff fo that 
kind in ppc platform supported by u-boot to pass device information to 
linux

Do we have a similar way for arm based platforms as well or any other
suggestions.

Regards
Vipin

[U-Boot] Peripheral multiplexing in devices

[Wolfgang Denk]

Dear Vipin KUMAR,

In message <4B9F89B2.8040101@st.com> you wrote:
> 
> Now, we want to support this in sw in such a way that we have a single
> image for linux for all possible configurations. We intend to do this
> though bootloader (u-boot in this case)

This may be possible, but it is not wise, nor the officially supported
mode of operation in U-Boot.  Please see bullet 2 at
http://www.denx.de/wiki/U-Boot/DesignPrinciples#KeepFast  and related
entries - U-Boot is not supposed to initialize things it does not need
for it's own operation.

> SPEAr has an arm platform and linux-arm doesn't seem to support peripheral
> multiplexing in the way we want. Though, I could see some stuff fo that 
> kind in ppc platform supported by u-boot to pass device information to 
> linux

We use the device tree to do things like this.

> Do we have a similar way for arm based platforms as well or any other
> suggestions.

Please check out Grant Likely's work to bring the device tree to ARM
Linux. 

Best regards,

Wolfgang Denk

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