AM4376: Regarding driver processing in Linux software when switching multiplexer devices

O.H

Part Number: AM4376
Other Parts Discussed in Thread: TMUX1574, SN3257-Q1,

Tool/software:

Hi experts,

The TI multiplexers TMUX1574 and SN3257-Q1 are listed as application examples for SPI multiplexers.
Enabling SPI-Based Flash Memory Expansion by Using Multiplexers (Rev. B) also discusses switching SPI connections, but could you please explain driver processing in Linux software?

In the diagram on the above, when two flash devices are multiplexed, the TI SDK (AM4376) initializes the SPI driver during kernel startup and reads the connected SPI flash.
However, if the multiplexer is subsequently switched to another device, it seems necessary to re-recognize (re-initialize?) the SPI flash.

In the diagram on the above, one of the MCUs is also disconnected, so I think some processing is required to recognize the connection.
Is it possible to re-recognize the SPI device using some command or register setting?

Best regrads,
O.H

1 month ago

0 Paula Carrillo 1 month ago

TI__Mastermind 39260 points

Hi O.H, which AM437x SDK are you using?

thank you

Paula

0 O.H 1 month ago in reply to Paula Carrillo

Mastermind 6340 points

Hi Paula,

Thank you for your response.

Paula Carrillo said:
which AM437x SDK are you using?

v06.03.00.106

Need to update to a newer version?

best regards,
O.H

0 Paula Carrillo 1 month ago in reply to O.H

TI__Mastermind 39260 points

Hi O.H, our latest AM437x Processor SDK is 9.3 (PROCESSOR-SDK-LINUX-AM437X Software development kit (SDK) | TI.com)

I am consulting, but I don't see any out-of-box way to dynamically switch between SPI's Linux driver devices.

One option to explore could be “Dynamic Device Tree Overlay”.

Thank you,

Paula

0 O.H 1 month ago in reply to Paula Carrillo

Mastermind 6340 points

Hi Paula,

Paula Carrillo said:
One option to explore could be “Dynamic Device Tree Overlay”.

Are there any materials for implementing "Dynamic Device Tree Overlay" on AM437x?

For AM62x, there is a "Static? (in u-boot) Device Tree Overlay" as shown below.
4.1.8. How to enable DT overlays in linux — Processor SDK AM62x Documentation

Also, the following thread states that "Dynamic Device Tree Overlay" is not supported, so please let me confirm this.
TMDX654IDKEVM: Device tree overlays - Processors forum - Processors - TI E2E support forums

Best regards,
O.H

0 Paula Carrillo 1 month ago in reply to O.H

TI__Mastermind 39260 points

Hi O.H, yes "Dynamic Device Tree Overlay" is not officially supported, so it would be experimental and probably complex to enable.

My understanding was that in your use case you need to switch between SPI devices at any time (reason of dynamic device tree overlay proposal). Please let me know if this is indeed the case, if not please help me to clarify your use case details.

Some additional information "Dynamic Device Tree Overlay" just for your reference:

thank you,

Paula

0 Andreas Dannenberg 1 month ago in reply to Paula Carrillo

TI__Guru 69652 points

Hi O.H,

let me chime in here too...

O.H said:
Is it possible to re-recognize the SPI device using some command or register setting?

For this the general principle should be the following...

Build the relevant drivers as loadable kernel modules (CONFIG_xxx=m rather than CONFIG_xxx=y)
When switching devices at runtime, do the following
1. Unmount any /dev/mtd devices associated with the SPI device
2. Unload the relevant drivers (flash driver, qspi driver) using `rmmod` or 'modprobe -r`
3. Trigger the exernal mux device by toggling a GPIO, etc.
4. Re-load the relevant drivers (`modprobe`). This should trigger a re-probe of the new flash device, based on flash IDs, etc.

A runtime modification to the device tree should only be needed if the layout of the new chip is different (partition sizes, etc.)

Regads, Andreas

0 O.H 1 month ago in reply to Andreas Dannenberg

Mastermind 6340 points

Hi Paula, Andreas,

Thnak you for your supports.

I will share the information you provided with the customer. I will contact you again if I have any additional questions.

Best regards,
O.H