Re: [PATCHv4 2/3] spi: Add spi driver for Socionext Synquacer platform

From: Trent Piepho <tpiepho@impinj.com>
To: "jassisinghbrar@gmail.com" <jassisinghbrar@gmail.com>,
	"linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>
Cc: "mark.rutland@arm.com" <mark.rutland@arm.com>,
	"jaswinder.singh@linaro.org" <jaswinder.singh@linaro.org>,
	"ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>,
	"broonie@kernel.org" <broonie@kernel.org>,
	"robh+dt@kernel.org" <robh+dt@kernel.org>,
	"masami.hiramatsu@linaro.org" <masami.hiramatsu@linaro.org>
Subject: Re: [PATCHv4 2/3] spi: Add spi driver for Socionext Synquacer platform
Date: Wed, 28 Feb 2018 17:55:55 +0000	[thread overview]
Message-ID: <1519840555.25567.218.camel@impinj.com> (raw)
In-Reply-To: <1519736330-3985-1-git-send-email-jassisinghbrar@gmail.com>

On Tue, 2018-02-27 at 18:28 +0530, jassisinghbrar@gmail.com wrote:
> From: Jassi Brar <jaswinder.singh@linaro.org>
> 
> This patch adds support for controller found on synquacer platforms.
> 
> Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
> ---
>  drivers/spi/Kconfig         |  11 +
>  drivers/spi/Makefile        |   1 +
>  drivers/spi/spi-synquacer.c | 663 ++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 675 insertions(+)
>  create mode 100644 drivers/spi/spi-synquacer.c
> 
> diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
> index 6037839..9e04bbe 100644
> --- a/drivers/spi/Kconfig
> +++ b/drivers/spi/Kconfig
> @@ -659,6 +659,17 @@ config SPI_SUN6I
>  	help
>  	  This enables using the SPI controller on the Allwinner A31 SoCs.
>  
> +config SPI_SYNQUACER
> +	tristate "Socionext's Synquacer HighSpeed SPI controller"
> +	depends on ARCH_SYNQUACER || COMPILE_TEST
> +	select SPI_BITBANG
> +	help
> +	  SPI driver for Socionext's High speed SPI controller which provides
> +	  various operating modes for interfacing to serial peripheral devices
> +	  that use the de-facto standard SPI protocol.
> +
> +	  It also supports the new dual-bit and quad-bit SPI protocol.
> +

As someone who designs and develops embedded Linux devices, it would be
really useful if there was a bit more documentation about the driver.

The hardware doesn't support DMA or even interrupts, and must busy wait
for the duration of the entire SPI transfers.  That's kind of a Big
Deal.  A design that involves lots of SPI transfers on a slow clock
will work fine on most SPI hardware, but will be utterly unfeasible
here.  It would be nice to say something about that.  I'd probably put
it in driver code.