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

From: Jassi Brar <jassisinghbrar@gmail.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Trent Piepho <tpiepho@impinj.com>,
	"linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"jaswinder.singh@linaro.org" <jaswinder.singh@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: Thu, 1 Mar 2018 19:41:02 +0530	[thread overview]
Message-ID: <CABb+yY3K+JjSMnxVPiEw-_RPUp47haqJy7KXuUUsDG=chQgwmQ@mail.gmail.com> (raw)
In-Reply-To: <CAKv+Gu-E82Fuj9hUjYLNvuDFQL0-MOSezVN-b8Ti7sU37Nooxw@mail.gmail.com>

On Thu, Mar 1, 2018 at 12:06 AM, Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
> On 28 February 2018 at 18:29, Jassi Brar <jassisinghbrar@gmail.com> wrote:
>> On Wed, Feb 28, 2018 at 11:25 PM, Trent Piepho <tpiepho@impinj.com> wrote:
>>> 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.
>>>
>> From marketing point of view, why would I want to advertise my limitations? :)
>>
>> Its not like any random platform might want to use this driver, nor
>> the enduser could do anything about it (its not a s/w issue). The
>> decision to integrate the ip in a SoC is already taken before the
>> driver is written. Obviously the users that need high spi performance
>> are not its intended target.
>>
>> BTW, the IP is actually not that bad. It is meant for interfacing
>> flash devices and can operate in two modes - "direct" mode where it
>> maps flash memory as i/o region and the other last resort "spi" mode
>> where we could manually drive the flash. This driver implements that
>> limited "spi" mode.
>>
>
> My SoC manual does list interrupts for this IP block. Are you sure
> SynQuacer uses the same version of the IP as before?
>
Having got hold of english specs, the newer version does seem to
support IRQ despite being named same "FIP006" as before.
Let me investigate deeper.

Thanks.