linux-kernel - Re: [PATCH 3/4] spi: s3c64xx: add gpio quirk for controller

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Date:	Thu, 7 Feb 2013 10:54:01 -0800
From:	Girish KS <girishks2000@...il.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	spi-devel-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/4] spi: s3c64xx: add gpio quirk for controller

On Thu, Feb 7, 2013 at 3:55 AM, Mark Brown
<broonie@...nsource.wolfsonmicro.com> wrote:
> On Tue, Feb 05, 2013 at 03:09:43PM -0800, Girish K S wrote:
>> This patch adds support for spi controllers with
>> dedicated clk/miso/mosi/cs pins. It skips the gpio
>> parsing and initialization for controllers that
>> have dedicated pins.
>
>>               if (sdd->tgl_spi != spi) { /* if last mssg on diff device */
>>                       /* Deselect the last toggled device */
>>                       cs = sdd->tgl_spi->controller_data;
>> -                     gpio_set_value(cs->line,
>> -                             spi->mode & SPI_CS_HIGH ? 0 : 1);
>> +                     if (!(sdd->port_conf->quirks & S3C64XX_SPI_QUIRK_GPIO))
>> +                             gpio_set_value(cs->line,
>> +                                     spi->mode & SPI_CS_HIGH ? 0 : 1);
>>               }
>
> This isn't going to work with system designs which ignore the /CS line
> the controller has and just use a GPIO instead.  This is very common,
> for example when connecting multiple devices to the same SPI bus.
As per grant's comment i would remove the quirk option and check for
"cs-gpio" property
to handle /CS. When multiple devices are connected to the same spi
bus, "cs-gpio" entry would exist in the dts
file, and works with /CS gpio lines.
>
> It seems like there's really two changes here.  One change is making the
> provision of pinmux information optional, the other is allowing the user
> to use the controller /CS management rather than using GPIO.
As suggested i would make two changes.
1. would parse the "gpios"  property and make decision whether to use
gpios/dedicated pins for miso/miso/clk.
2.would parse "cs-gpio"  property from dts node to handle the chip select
correct me if my understanding is wrong
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