Re: spi-pl022 on lpc32xx

[Vladimir Zapolskiy <vz@mleia.com>]

Hi Trevor,

On 3/28/22 22:01, Trevor Woerner wrote:
> Hi,
> 
> I have a spi-nor chip (m25p16) connected to the SPI1 bus of an LPC32xx-based
> machine that I can't get working.
> 
> The LPC32xx has both an SPI controller and an SSP controller, but only one can
> be active at a time. The SSP is an ARM primecell component which is a "SPI on
> steroids" device. The SSP can be run in several modes, one of which is "SPI"
> mode.
> 
> The LPC32xx machine does not have a SPI driver in the kernel, but it does have
> a driver for the SSP controller. Since there is no SPI driver, I'm using the
> SSP driver in "SPI" mode, but not having much luck.

I have a feeling that Sylvain Lemieux once reported that the PrimeCell SPI
driver worked for him, but here I might be wrong.

> I can see the SPI subsystem sending the 0x9f command (READ ID), the spi-pl022
> driver writes the command to the SSP data register, but the flag in the SSP
> status register to say data has been received never goes up.
> 
> I'm wondering if anyone is successfully using the current spi-pl022 driver to
> interact with an SPI device (preferably on a lpc32xx-based machine)?
> 
> I've spent the better part of the last week poking at this. I've tried many
> combinations of device tree, but what I think should work is:
> 
> 	&ssp0 {
> 		status = "okay";
> 		num-cs = <1>;
> 		cs-gpios = <&gpio 3 4 1>;
> 
> 		m25p16@0 {
> 			compatible = "jedec,spi-nor";
> 			reg = <0>;
> 			spi-max-frequency = <500000>;
> 
> 			pl022,interface = <0>;
> 			pl022,com-mode = <1>;
> 		};
> 	};
> 

FWIW on my board I do use both SSP0 and SSP1 at once, but I didn't rebase
the dts/kernel for a long time, so the examples might be outdated:

&ssp0 {
	num-cs = <1>;
	cs-gpios = <&gpio 3 5 GPIO_ACTIVE_HIGH>; /* SSEL0 */

	sc16is752@0 {
		compatible = "nxp,sc16is752";
		reg = <0>;
		spi-max-frequency = <4000000>;

		/* 18.432 MHz external oscillator */
		clocks = <&xtal_18432k>;

		/* Interrupt to GPI_07 */
		interrupt-parent = <&sic2>;
		interrupts = <15 IRQ_TYPE_EDGE_FALLING>;
	};
};

&ssp1 {
	num-cs = <1>;
	cs-gpios = <&gpio 3 4 GPIO_ACTIVE_HIGH>;

	s25fl216k@0 {
		compatible = "s25fl216k", "jedec,spi-nor";
		reg = <0>;
		spi-max-frequency = <150000>;
		spi-cpol;
		spi-cpha;
	};
};

Also SSP0 is enabled on PhyTec phy3250 board, there is an at25 eeprom on it,
I've just briefly checked the device tree node, and apparently it contains
some references/properties specific to the PL022 SPI driver.

> I've tried a couple other compatible strings ("micron,m25p16", "st,m25p16"),
> I've tried a range of frequencies (from 0.5MHz to 33MHz). The 3 options for
> interface are 0 (SPI), 1 (TI), or 2 (Microwire) and I've tried all of them. I
> don't believe the DMA system works generically on the lpc32xx but I've tried
> both interrupt <0> and polling <1> for the com-mode. I believe SPI1 and SSP0
> are the same and SPI2 and SSP1 are the same (which is why I'm using SSP0
> here).
> 
> The pl-022 driver is quite aggressive about shutting off the SSP and raising
> the chip select after a message is sent, so I modified my driver to leave the
> SSP enabled and keeping the (active-low) chip select low (in case those were
> affecting the reply) but there's no change.
> 
> One thing that's curious is that the platform_info->bus_id is -1. This bus
> number comes from the parent device (spi core). I wonder if this driver is not
> registering itself correctly with the spi core?
> 
> Best regards,
>   	Trevor

--
Best wishes,
Vladimir