linux-kernel - Re: [PATCH v2] spi: mt7621: allow GPIO chip select lines

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Message-ID: <ff184df8-1917-456b-97c8-bc270987bd55@collabora.com>
Date: Mon, 18 Mar 2024 11:16:05 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Justin Swartz <justin.swartz@...ingedge.co.za>,
 Mark Brown <broonie@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>
Cc: linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v2] spi: mt7621: allow GPIO chip select lines

Il 16/03/24 02:03, Justin Swartz ha scritto:
> Extract a magic number, from mt7621_spi_probe(), used to
> declare the number of chip select lines (which co-incides
> with the native chip select count of 2) to a macro.
> 
> Use the newly defined MT7621_NATIVE_CS_COUNT macro to
> instead populate both the spi_controller's max_native_cs
> and num_chipselect members.
> 
> Declare that the spi_controller should use_gpio_descriptors
> if present in the device properties (such as those declared
> in the cs-gpio property of a "ralink,mt7621-spi" compatible
> device-tree node) so that the SPI core will recalculcate
> num_chipselect to account for the GPIO descriptors that
> it should have populated in the cs_gpiod array member.
> 
> Remove the assignment of mt7621_spi_transfer_one_message()
> to the spi_controller's transfer_one_message hook.
> 
> Refactor the mt7621_spi_transfer_one_message() logic into
> mt7621_spi_prepare_message() and mt7621_spi_transfer_one()
> and assign both to the spi_controller's prepare_message
> and transfer_one hooks respectively.
> 
> Migrate the call mt7621_spi_transfer_one_message() made to
> mt7621_spi_flush() just before chip select deactivation,
> to the end of mt7621_spi_write_half_duplex() to ensure
> that any pending data is shifted out of MOSI before the SPI
> core deactivates the chip select line.
> 
> As chip select activation is now taken care of by the SPI
> core, due to the use of the transfer_one hook instead of
> transfer_one_message, the calls to mt7621_spi_set_cs()
> from mt7621_spi_transfer_one_message() have fallen away.
> 
> And although the SPI core will handle activation for GPIO
> chip select lines behind the scenes, it requires a callback
> to allow the driver to perform controller-specific
> operations to control its native chip select lines.
> 
> Rename mt7621_spi_set_cs() to mt7621_spi_set_native_cs()
> and make sure that it takes into account the activation
> polarity of the chip select line it's acting upon, as the
> passed enable parameter represents the desired line level
> and not the desired activation state, and then assign
> mt7621_set_cs() to the spi_controller's set_cs hook.
> 
> Signed-off-by: Justin Swartz <justin.swartz@...ingedge.co.za>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>