linux-kernel - Re: [PATCH v3 5/6] spi: at91-usart: add driver for at91-usart as spi

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Message-ID: <20180524175620.GB12093@piout.net>
Date:   Thu, 24 May 2018 19:56:20 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Radu Pirea <radu.pirea@...rochip.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Richard Genoud <richard.genoud@...il.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>
Subject: Re: [PATCH v3 5/6] spi: at91-usart: add driver for at91-usart as spi

Hi,

On 24/05/2018 19:04:11+0300, Radu Pirea wrote:
> 
> 
> On 05/17/2018 07:54 AM, Mark Brown wrote:
> > On Tue, May 15, 2018 at 12:22:24PM +0300, Radu Pirea wrote:
> > > On Mon, 2018-05-14 at 20:38 +0300, Andy Shevchenko wrote:
> > 
> > > > So, what is not going as expected in "SPI core takes care of CSs"
> > > > case?
> > > > Did you use oscilloscope for that?
> > 
> > > Yes, I used and CSs was not asserted. Anyway, I will will try again.
> > 
> > If the core chip select handling is not working properly for some reason
> > then the core chip select handling should be fixed rather than just open
> > coding in your driver - probably it's also broken for other users.
> > 
> 
> Hi Mark,
> 
> I found the fix for cs-gpios. If I change spi_add_device function like
> this(see below) everything is ok.
> 
> int spi_add_device(struct spi_device *spi)
> 
> ...
> 
>     if (ctlr->cs_gpios){
>         spi->cs_gpio = ctlr->cs_gpios[spi->chip_select];
>         if(gpio_is_valid(spi->cs_gpio))
>             gpio_direction_output(spi->cs_gpio, !(spi->mode & SPI_CS_HIGH));
> 
>     }
> 
> ...
> 
>     return status;
> }
> 
> In the subsystem gpio direction of pins is never set and gpio_set_value()
> don't set the direction.
> In my opinion gpio_direction_output() set direction should be called in
> spi_add_device. What do you think? Is ok?

Back in 2014, I was suggesting using devm_gpio_request_one() in
of_spi_register_master(). That would take care of setting the direction
of the GPIO:

https://www.spinics.net/lists/arm-kernel/msg351251.html

I never took the time to create the patch and test though.

-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com