不同芯片上的相同Linux驱动程序

Question

I am newbie on linux driver development. I wonder how same linux drivers work on different chips. For instance, same uart driver work on allwinner and sitara socs?Do allwinner and sitara socs have same uart peripheral?

Answer 1

Basically how things are working is based on layering concept as shown below in Image.

Kernel source is layered so that we don't have to write it again and again for every system and to increase its re usability.

Approach behind this is, architect depended code on bottom layer, then comes layer of bus drivers (SPI, I2C, etc.) and then comes adapter or device drivers.

So suppose if a board is using company A's NAND Flash over SPI or any similar interface, we can use same device driver for this company A - NAND Flash on any given board, irrespective of whatever SPI apapter present, but only thing need to be concerned is SPI bus driver should be present as platform driver.

Here while probing, SPI will give access to the device driver with NAND Flash's Address. Here SPI driver knows how to communicate with SPI devices and NAND Flash driver keep on telling to SPI Driver what to transfer to NAND flash and SPI takes responsibility for how to transfer. In this SPI Platform driver may differ with different platforms but NAND Flash driver remains same.

With this approach same device driver for a device can be used in different systems without any dependencies for hardware specification.

Answer 2

Well, at first, it doesn't matter what SoC is, or who is the vendor. What matters is the UART peripheral only. So if the peripheral has got some registers on SoC A and exact same registers on SoC B, both of them can go with the same driver. The driver would just tell the underlying bus ( which is usually managed by a different subsystem) to write some configuration bits to specified registers for different operations. Also, usually if a chip is derived from some old model, simple peripherals like UART remain pretty much the same.

Next .. If all the Allwiner SoCs has the same UART ? Not sure about all of them but this here [ https://github.com/allwinner-zh/linux-3.4-sunxi/blob/master/drivers/tty/serial/Kconfig ] suggests that most of the SoCs use the same UARTs.

And about Sitara Soc, they have shifted to 8250 driver [ http://processors.wiki.ti.com/index.php/Sitara_Linux_UART_-_Switching_to_8250_Driver] , which has been used for many years now. So yeah, since its they (TI) who have decided to this, they will have to maintain backward compatibility in terms of UART.