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From:   Carlo Caione <carlo@caione.org>
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Date:   Fri, 18 Nov 2022 20:02:32 +0100
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Subject: Re: [PATCH 2/3] drm/tiny: ili9486: Do not assume 8-bit only SPI
 controllers
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To:     Mark Brown <broonie@kernel.org>
Cc:     Kamlesh Gurudasani <kamlesh.gurudasani@gmail.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Jerome Brunet <jbrunet@baylibre.com>,
        David Airlie <airlied@gmail.com>,
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        Kevin Hilman <khilman@baylibre.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        linux-arm-kernel@lists.infradead.org,
        linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-spi@vger.kernel.org, dri-devel@lists.freedesktop.org
References: <20221116-s905x_spi_ili9486-v1-0-630401cb62d5@baylibre.com>
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On 18/11/2022 16:44, Mark Brown wrote:

>> The problem arrives when your controller does support 16-bits, so 
>> your data is not swapped, but you still put the data on the bus 
>> with 8-bit transfers.
> 
> Why would you need to use 8 bit transfers if the controller supports
>  16 bits?

No idea why this driver is forcing 8-bit transfers when the controller
supports 16-bits (this is what this patch is fixing).

My theory is that this driver was written with the Raspberry Pi HATs in
mind and (AFAICT) the RPi has an 8-bit only SPI controller so the driver
author didn't bother with anything different.

--
Carlo Caione