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List:       linux-tegra
Subject:    RE: [PATCH V3 5/9] spi: export spi core function spi_set_cs
From:       Sowjanya Komatineni <skomatineni () nvidia ! com>
Date:       2019-04-29 22:02:46
Message-ID: BYAPR12MB3398D133D1C71355BC530754C2390 () BYAPR12MB3398 ! namprd12 ! prod ! outlook ! com
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> On Mon, Apr 15, 2019 at 02:30:30PM -0700, Sowjanya Komatineni wrote:
> > This patch exports spi_set_cs of the spi core to allow SPI masters to 
> > use when gpio based chip select is needed.
> 
> This isn't really what I meant when I said it'd be good to use the core GPIO code - \
> this function doesn't do a huge amount really and the usage of it in your \
> subsequent patch for the > driver isn't exactly joined up with the little it does \
> (which is mainly swapping in the GPIO chip select instead of the hardware chip \
> select) isn't used in your driver usage of this as far as I can see.  The bulk of \
> the chip select handling code in the core is actually in transfer_one_message() \
> which your driver doesn't use as it's got it's own implementation of that; I've not \
> looked in enough detail to figure out if it could use it. 
> 
> 
In SPI Tegra driver, we wanted to have GPIO based CS control when cs-gpios is \
specified in parallel to HW/SW CS. Having parallel GPIO based CS is to mimic some of \
the timing stuff that's needed for some spi devices by not actually using HW CS on \
platform but only for SPI HW design logic inside the chip.

Tegra spi driver don't use set_cs callback so looking into spi_set_cs from spi core \
implementation when cs-gpios property is used it exactly the same that is needed for \
GPIO control CS. So used this in V3. 

Can you please provide more details on what you are suggesting?
Do you prefer not to use SPI core spi_set_cs and gpio_set_values APIs and instead \
implement in tegra SPI driver using GPIO descriptors ?

Thanks
Sowjanya


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