Sharing the same SPI between two devices.

Sharing the same SPI between two devices.

[Patryk]

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Hi, I want to have two devices on the same SPI bus.

These devices are:

- SPI nor flash (QSPI compatible)

- my custom device (SPI compatible).

For SPI NOR flash I have the driver in the kernel, for my custom device I
do not have such a driver.

My question is - how the access to this particular SPI peripheral can be
serialized between these two drivers in order to prevent simultaneous
access that would result in a mess on the SPI? Do I have to modify the
existing driver for SPI NOR flash or not?

How about different configurations for these devices - as I mentioned one
is QSPI compatible whereas the other one is SPI compatible. Can I
reconfigure the SPI bus driver before each "transaction"?


Best regards

Patryk

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Re: Sharing the same SPI between two devices.

[Lucas Tanure]

On Thu, Nov 2, 2023 at 9:15 AM Patryk <pbiel7@gmail.com> wrote:
>
> Hi, I want to have two devices on the same SPI bus.
>
> These devices are:
>
> - SPI nor flash (QSPI compatible)
>
> - my custom device (SPI compatible).
>
> For SPI NOR flash I have the driver in the kernel, for my custom device I do not have such a driver.
>
> My question is - how the access to this particular SPI peripheral can be serialized between these two drivers in order to prevent simultaneous access that would result in a mess on the SPI? Do I have to modify the existing driver for SPI NOR flash or not?
>
> How about different configurations for these devices - as I mentioned one is QSPI compatible whereas the other one is SPI compatible. Can I reconfigure the SPI bus driver before each "transaction"?
>
>
> Best regards
>
> Patryk
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies@kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

To share the SPI bus between two devices just put them difirent chip
select pins.
Can you use regmap for what you trying to do?

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Re: Sharing the same SPI between two devices.

[Billie Alsup (balsup)]

> My question is - how the access to this particular SPI peripheral can be serialized between these two drivers in order to prevent simultaneous access that would result in a mess on the SPI? Do I have to modify the existing driver for SPI NOR flash or not? 

Doesn't the serialization happen at the SPI "master" controller driver level, i.e. the device registered via devm_spi_register_master (or equivalent)?  The spi-nor driver is a layer making requests to the underlying controller driver, which come as requests via various callbacks (e.g. transfer_one, prepare_message, mem_ops).  It is that driver that should be serializing requests from higher layers.  Shouldn't your "other" driver be making similar requests of the underlying controller?

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