linux-kernel - Re: [PATCH v1] Input: ads7846: do not overwrite spi->mode flags set by spi framework

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Date:   Tue, 27 Oct 2020 09:07:19 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>,
        David Jander <david@...tonic.nl>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>
Subject: Re: [PATCH v1] Input: ads7846: do not overwrite spi->mode flags set
 by spi framework

On Mon, Oct 26, 2020 at 08:53:09PM -0700, Dmitry Torokhov wrote:
> On Thu, Oct 22, 2020 at 08:54:02AM +0200, Oleksij Rempel wrote:
> > On Wed, Oct 21, 2020 at 11:27:57AM -0700, Dmitry Torokhov wrote:
> > > On Wed, Oct 21, 2020 at 12:56:14PM +0200, Oleksij Rempel wrote:
> > > > 
> > > > As you can see, I would need to configure my dts with spi-cs-high flag,
> > > > even if the hardware is actually ACTIVE_LOW. If I will go this way, I
> > > > would risk a regression as soon as this issue is fixed.
> > > > 
> > > > Since the spi framework is already parsing devicetree and set all needed
> > > > flags, I assume it is wrong to blindly drop all this flags in the
> > > > driver.
> > > 
> > > Yes, but I wonder if the devices can only work in mode 0 we should be
> > > doing:
> > > 
> > > 	spi->mode &= ~SPI_MODE_MASK; // to be defined as 0x03 in spi.h
> > > 	spi->mode |= SPI_MODE_0;
> > > 
> > > as we can't simply "or" mode value as is
> > 
> > Why not? This values are taken from device tree. If some developer
> > decided to add them, then driver should take it over. Even if this
> > values will break the functionality.
> > 
> > Other properties of this driver will break the functionality too of this
> > driver too, so why should we silently filter only set of this bits?
> 
> What I was trying to say is that if driver wants to set mode to
> particular value it should not "or" the value, as it will not reset the
> relevant bits. I.e. if there some undesirable data in spi->mode mode
> bits it will not get set properly by essentially doing "spi->mode |= 0".
> That is why I said the driver needs to clear mode bits and set them to
> the desired mode.

Ok, i'll update this patch as you suggested.

Regards,
Oleksij
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