linux-kernel - Re: [PATCH RFC v3 2/9] spi: add basic support for SPI offloading

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Message-ID: <20240803105809.1b36287d@jic23-huawei>
Date: Sat, 3 Aug 2024 10:58:09 +0100
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>, 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
Subject: Re: [PATCH RFC v3 2/9] spi: add basic support for SPI offloading

On Tue, 30 Jul 2024 14:35:09 -0500
David Lechner <dlechner@...libre.com> wrote:

> On 7/27/24 8:15 AM, Jonathan Cameron wrote:
> > On Mon, 22 Jul 2024 16:57:09 -0500
> > David Lechner <dlechner@...libre.com> wrote:
> >   
> 
> 
> >> +/**
> >> + * spi_offload_prepare - prepare offload hardware for a transfer
> >> + * @spi:	The spi device to use for the transfers.
> >> + * @id:		Function ID if SPI device uses more than one offload or NULL.
> >> + * @msg:	The SPI message to use for the offload operation.
> >> + *
> >> + * Requests an offload instance with the specified ID and programs it with the
> >> + * provided message.
> >> + *
> >> + * The message must not be pre-optimized (do not call spi_optimize_message() on
> >> + * the message).
> >> + *
> >> + * Calls must be balanced with spi_offload_unprepare().
> >> + *
> >> + * Return: 0 on success, else a negative error code.
> >> + */
> >> +int spi_offload_prepare(struct spi_device *spi, const char *id,
> >> +			struct spi_message *msg)
> >> +{
> >> +	struct spi_controller *ctlr = spi->controller;
> >> +	int ret;
> >> +
> >> +	if (!ctlr->offload_ops)
> >> +		return -EOPNOTSUPP;
> >> +
> >> +	msg->offload = true;  
> > I'd set this later perhaps as...  
> 
> If we move it, then we would have to create a new function
> to call instead of spi_optimize_message() so that the controller
> driver can know that this is an offload message and not a
> regular message since they will need to be handled differently
> during the optimization phase.
Ah. I'd missed that.
> 
> >> +
> >> +	ret = spi_optimize_message(spi, msg);
> >> +	if (ret)  
> > 
> > It otherwise needs clearing here so it doesn't have side
> > effects if an error occurs.

Then it needs clearing here I think.

> >   
> >> +		return ret;
> >> +
> >> +	mutex_lock(&ctlr->io_mutex);
> >> +	ret = ctlr->offload_ops->prepare(spi, id, msg);
> >> +	mutex_unlock(&ctlr->io_mutex);
> >> +
> >> +	if (ret) {
> >> +		spi_unoptimize_message(msg);
> >> +		msg->offload = false;
> >> +		return ret;
> >> +	}
> >> +
> >> +	return 0;
> >> +}
> >> +EXPORT_SYMBOL_GPL(spi_offload_prepare);  
> >