linux-kernel - Re: [PATCH v5 06/16] spi: add offload TX/RX streaming APIs

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Message-ID: <259515cc-ca36-4dcd-b884-a9f9e3c2ab2e@baylibre.com>
Date: Sun, 24 Nov 2024 11:54:44 -0600
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Nuno Sá <nuno.sa@...log.com>,
 Uwe Kleine-König <ukleinek@...nel.org>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Lars-Peter Clausen <lars@...afoo.de>, David Jander <david@...tonic.nl>,
 Martin Sperl <kernel@...tin.sperl.org>, linux-spi@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-iio@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v5 06/16] spi: add offload TX/RX streaming APIs

On 11/24/24 10:50 AM, Jonathan Cameron wrote:
> On Fri, 15 Nov 2024 14:18:45 -0600
> David Lechner <dlechner@...libre.com> wrote:
> 
>> Most configuration of SPI offloads is handled opaquely using the offload
>> pointer that is passed to the various offload functions. However, there
>> are some offload features that need to be controlled on a per transfer
>> basis.
>>
>> This patch adds a flag field to struct spi_transfer to allow specifying
>> such features. The first feature to be added is the ability to stream
>> data to/from a hardware sink/source rather than using a tx or rx buffer.
>> Additional flags can be added in the future as needed.
>>
>> A flags field is also added to the offload struct for providers to
>> indicate which flags are supported. This allows for generic checking of
>> offload capabilities during __spi_validate() so that each offload
>> provider doesn't have to implement their own validation.
>>
>> As a first users of this streaming capability, getter functions are
>> added to get a DMA channel that is directly connected to the offload.
>> Peripheral drivers will use this to get a DMA channel and configure it
>> to suit their needs.
>>
>> Signed-off-by: David Lechner <dlechner@...libre.com>
> Some docs that need updating.  Otherwise I wonder if we should delay
> the _tx variants until there is a driver using them.
> 
> I'm sure you have one on the way and there is an argument that it makes
> sense to review rx and tx together, but still good to only add code
> when it's used.
> 
> Jonathan
> 

In v1 Mark commented that he expected TX along with RX. And we do
have a DAC driver we can probably add to the series in the next
revision that uses it.