Re: [PATCH] spi: imx: Don't expect DMA for i.MX{25, 35, 50, 51, 53} cspi devices

[Martin Kaiser <martin@kaiser.cx>]

Hello,

Thus wrote Uwe Kleine-König (u.kleine-koenig@pengutronix.de):

> Hello,

> On Fri, May 10, 2024 at 02:32:56PM +0200, Uwe Kleine-König wrote:
> > On Wed, May 08, 2024 at 03:44:53PM +0200, Martin Kaiser wrote:
> > > Thus wrote Uwe Kleine-König (u.kleine-koenig@pengutronix.de):
> > > > While in commit 2dd33f9cec90 ("spi: imx: support DMA for imx35") it was
> > > > claimed that DMA works on i.MX25, i.MX31 and i.MX35 the respective
> > > > device trees don't add DMA channels. The Reference manuals of i.MX31 and
> > > > i.MX25 also don't mention the CSPI core being DMA capable. (I didn't
> > > > check the others.)

> > > If I'm not mistaken, the imx25 reference manual

> > > https://www.nxp.com/docs/en/reference-manual/IMX25RM.pdf

> > > does say that CSPI has DMA support. Section 18.1.1 (Features) lists DMA as one
> > > of the features. There's also DMA events (section 3) for CSPI-1/2/3 RX, TX.

> > Oh indeed. I don't know what made me claim that DMA isn't mentioned in
> > the reference manual. Maybe I looked at the i2c chapter.

> > I now did:

> > diff --git a/arch/arm/boot/dts/nxp/imx/imx25.dtsi b/arch/arm/boot/dts/nxp/imx/imx25.dtsi
> > index 4a85684deff8..710b28a41bae 100644
> > --- a/arch/arm/boot/dts/nxp/imx/imx25.dtsi
> > +++ b/arch/arm/boot/dts/nxp/imx/imx25.dtsi
> > @@ -190,6 +190,8 @@ spi1: spi@43fa4000 {
> >  				reg = <0x43fa4000 0x4000>;
> >  				clocks = <&clks 78>, <&clks 78>;
> >  				clock-names = "ipg", "per";
> > +				dmas = <&sdma 8 1 0>, <&sdma 9 1 0>;
> > +				dma-names = "rx", "tx";
> >  				interrupts = <14>;
> >  				status = "disabled";
> >  			};
> > @@ -229,6 +231,8 @@ spi3: spi@50004000 {
> >  				interrupts = <0>;
> >  				clocks = <&clks 80>, <&clks 80>;
> >  				clock-names = "ipg", "per";
> > +				dmas = <&sdma 34 1 0>, <&sdma 35 1 0>;
> > +				dma-names = "rx", "tx";
> >  				status = "disabled";
> >  			};

> > @@ -257,6 +261,8 @@ spi2: spi@50010000 {
> >  				reg = <0x50010000 0x4000>;
> >  				clocks = <&clks 79>, <&clks 79>;
> >  				clock-names = "ipg", "per";
> > +				dmas = <&sdma 6 1 0>, <&sdma 7 1 0>;
> > +				dma-names = "rx", "tx";
> >  				interrupts = <13>;
> >  				status = "disabled";
> >  			};

> Additionally to the above I now did:

> diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
> index c3e5cee18bea..74da1a965a0d 100644
> --- a/drivers/spi/spi-imx.c
> +++ b/drivers/spi/spi-imx.c
> @@ -1428,12 +1428,9 @@ static int spi_imx_dma_transfer(struct spi_imx_data *spi_imx,
>  	if (ret)
>  		goto dma_failure_no_start;

> -	if (!spi_imx->devtype_data->setup_wml) {
> -		dev_err(spi_imx->dev, "No setup_wml()?\n");
> -		ret = -EINVAL;
> -		goto dma_failure_no_start;
> +	if (spi_imx->devtype_data->setup_wml) {
> +		spi_imx->devtype_data->setup_wml(spi_imx);
>  	}
> -	spi_imx->devtype_data->setup_wml(spi_imx);

>  	/*
>  	 * The TX DMA setup starts the transfer, so make sure RX is configured


> because there is no .setup_wml() callback for i.MX25 in
> imx31_cspi_devtype_data and the DMA register is already setup in
> mx31_prepare_transfer(). Without this change DMA isn't used.

> However this breaks SPI transfers, when I try to read out an MRAM I get:

> 	root@ecu02:~ hexdump -C /dev/mtd4
> 	[   71.813807] spi_imx 43fa4000.spi: I/O Error in DMA TX
> 	[   71.819173] spi-nor spi0.2: SPI transfer failed: -110
> 	[   71.829129] spi_master spi0: failed to transfer one message from queue
> 	[   71.843962] spi_master spi0: noqueue transfer failed

> So it would indeed be interesting if you ever managed to use DMA on
> i.MX25.

I believe so. Looking into my notes from 2016 (when I last tried this), I got
the -110 error when the SMC bit in CONREG wasn't set. But this should now be
done in mx31_prepare_transfer if DMA is used...

I'll try to set up a test some time next week.

Best regards,
Martin