Re: [PATCH 2/2] spi: Add Baikal-T1 System Boot SPI Controller driver

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Fri, May 8, 2020 at 12:37 PM Serge Semin
<Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> This SPI-controller is a part of the Baikal-T1 System Controller and
> is based on the DW APB SSI IP-core, but with very limited resources:
> no IRQ, no DMA, only a single native chip-select and just 8 bytes Tx/Rx
> FIFO available. In order to provide a transparent initial boot code
> execution this controller is also utilized by an vendor-specific block,
> which provides an CS0 SPI flash direct mapping interface. Since both
> direct mapping and SPI controller normal utilization are mutual exclusive
> only a one of these interfaces can be used to access an external SPI
> slave device. Taking into account the peculiarities of the controller
> registers and physically mapped SPI flash access, very limited resources
> and seeing the normal usecase of the controller is to access an external
> SPI-nor flash, we decided to create a dedicated SPI driver for it.

It seems a lot of code.
Why can't you use spi-dw-mmio.c et al.?

> The driver provides callbacks for native messages-based SPI interface,
> SPI-memory and direct mapping read operations. Due to not having any
> asynchronous signaling interface provided by the core we have no choice
> but to implement a polling-based data transmission/reception algorithm.
> In addition to that in order to bypass the automatic native chip-select
> toggle the driver disables the local interrupts during the memory-based
> transfers if no complementary GPIO-based chip-select detected in the
> platform.



-- 
With Best Regards,
Andy Shevchenko