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

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Message-ID: <20241125213058.137349ed@jic23-huawei>
Date: Mon, 25 Nov 2024 21:30:58 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
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 Sun, 24 Nov 2024 11:54:44 -0600
David Lechner <dlechner@...libre.com> wrote:

> 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.
Perfect, or maybe just reference that in the description as
'coming soon'.  I'm fine with infrastructure coming a bit before the
user and I can always trust you to send me more drivers :)

Jonathan