linux-kernel - Re: [PATCH v14 1/2] fpga: lattice-sysconfig-spi: add Lattice sysCONFIG FPGA manager

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Date:   Thu, 6 Oct 2022 14:09:04 +0300
From:   Ivan Bornyakov <i.bornyakov@...rotek.ru>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     mdf@...nel.org, hao.wu@...el.com, yilun.xu@...el.com,
        trix@...hat.com, dg@...ix.com, j.zink@...gutronix.de,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        devicetree@...r.kernel.org, system@...rotek.ru,
        linux-fpga@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH v14 1/2] fpga: lattice-sysconfig-spi: add Lattice
 sysCONFIG FPGA manager

On Thu, Oct 06, 2022 at 10:18:01AM +0200, Marc Kleine-Budde wrote:
> On 06.10.2022 10:44:48, Ivan Bornyakov wrote:
> > Add support to the FPGA manager for programming Lattice ECP5 FPGA over
> > slave SPI sysCONFIG interface.
> > 
> > sysCONFIG interface core functionality is separate from both ECP5 and
> > SPI specifics, so support for other FPGAs with different port types can
> > be added in the future.
> > 
> > Signed-off-by: Ivan Bornyakov <i.bornyakov@...rotek.ru>
> > ---
> 
> [...]
> 
> > +static int sysconfig_spi_bitstream_burst_init(struct sysconfig_priv *priv)
> > +{
> > +	const u8 lsc_bitstream_burst[] = SYSCONFIG_LSC_BITSTREAM_BURST;
> 
> I think you're not allowed to use stack memory for SPI transfers. Better
> clarify this with the SPI people.
> 

You are right. Documentation/spi/spi-summary.rst says:

  - Follow standard kernel rules, and provide DMA-safe buffers in
    your messages.

Thanks for pointing out.

> > +	struct spi_device *spi = to_spi_device(priv->dev);
> > +	struct spi_transfer xfer = {
> > +		.tx_buf = lsc_bitstream_burst,
> > +		.len = sizeof(lsc_bitstream_burst),
> > +		.cs_change = 1,
> > +	};
> > +	struct spi_message msg;
> > +	int ret;
> > +
> > +	spi_message_init_with_transfers(&msg, &xfer, 1);
> > +
> > +	/*
> > +	 * Lock SPI bus for exclusive usage until FPGA programming is done.
> > +	 * SPI bus will be released in sysconfig_spi_bitstream_burst_complete().
> > +	 */
> > +	spi_bus_lock(spi->controller);
> > +
> > +	ret = spi_sync_locked(spi, &msg);
> > +	if (ret)
> > +		spi_bus_unlock(spi->controller);
> > +
> > +	return ret;
> > +}
> 
> regards,
> Marc
> 
> -- 
> Pengutronix e.K.                 | Marc Kleine-Budde           |
> Embedded Linux                   | https://www.pengutronix.de  |
> Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
> Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |