linux-kernel - Re: [PATCH v2 4/6] spi: axi-spi-engine: support SPI_MULTI_BUS_MODE

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Message-ID: <0e59d92f-7b3c-4ff6-b3ad-7fae2ded9b77@baylibre.com>
Date: Wed, 12 Nov 2025 10:59:56 -0600
From: David Lechner <dlechner@...libre.com>
To: Marcelo Schmitt <marcelo.schmitt1@...il.com>
Cc: Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Marcelo Schmitt <marcelo.schmitt@...log.com>,
 Michael Hennerich <michael.hennerich@...log.com>,
 Nuno Sá <nuno.sa@...log.com>,
 Jonathan Cameron <jic23@...nel.org>, Andy Shevchenko <andy@...nel.org>,
 Sean Anderson <sean.anderson@...ux.dev>, linux-spi@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-iio@...r.kernel.org
Subject: Re: [PATCH v2 4/6] spi: axi-spi-engine: support
 SPI_MULTI_BUS_MODE_STRIPE

On 11/11/25 9:12 AM, Marcelo Schmitt wrote:
> Hi David,
> 
> The updates to spi-engine driver look good.
> Only one comment about what happens if we have conflicting bus modes for the
> offload case. Just to check I'm getting how this is working.
> 

...

>> @@ -284,6 +316,24 @@ static int spi_engine_precompile_message(struct spi_message *msg)
>>  			min_bits_per_word = min(min_bits_per_word, xfer->bits_per_word);
>>  			max_bits_per_word = max(max_bits_per_word, xfer->bits_per_word);
>>  		}
>> +
>> +		if (xfer->rx_buf || xfer->offload_flags & SPI_OFFLOAD_XFER_RX_STREAM ||
>> +		    xfer->tx_buf || xfer->offload_flags & SPI_OFFLOAD_XFER_TX_STREAM) {
>> +			switch (xfer->multi_bus_mode) {
>> +			case SPI_MULTI_BUS_MODE_SINGLE:
>> +			case SPI_MULTI_BUS_MODE_STRIPE:
>> +				break;
>> +			default:
>> +				/* Other modes, like mirror not supported */
>> +				return -EINVAL;
>> +			}
>> +
>> +			/* If all xfers have the same multi-bus mode, we can optimize. */
>> +			if (multi_bus_mode == SPI_ENGINE_MULTI_BUS_MODE_UNKNOWN)
>> +				multi_bus_mode = xfer->multi_bus_mode;
>> +			else if (multi_bus_mode != xfer->multi_bus_mode)
>> +				multi_bus_mode = SPI_ENGINE_MULTI_BUS_MODE_CONFLICTING;
> 
> Here we check all xfers have the same multi-bus mode and keep the mode that has
> been set. Otherwise, we set this conflicting mode and the intent is to generate
> SDI and SDO mask commands on demand on spi_engine_precompile_message(). OTOH,

s/spi_engine_precompile_message/spi_engine_compile_message/

Probably just a typo, but just to be clear, the "on demand" bit happens in the
compile function rather than precompile.

> if all xfers have the same multi-bus mode, we can add just one pair of SDI/SDO
> mask commands in spi_engine_trigger_enable() and one pair latter in
> spi_engine_trigger_disable(). I guess this is the optimization mentioned in the
> comment.
> 
Your understanding is correct.