linux-kernel - Re: [PATCH v4 05/11] dmaengine: Introduce DMA-device device

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Date:   Fri, 29 May 2020 15:12:03 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Vinod Koul <vkoul@...nel.org>, Viresh Kumar <vireshk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>, linux-mips@...r.kernel.org,
        devicetree@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 05/11] dmaengine: Introduce DMA-device device_caps
 callback

On Fri, May 29, 2020 at 01:23:55AM +0300, Serge Semin wrote:
> There are DMA devices (like ours version of Synopsys DW DMAC) which have
> DMA capabilities non-uniformly redistributed amongst the device channels.
> In order to provide a way of exposing the channel-specific parameters to
> the DMA engine consumers, we introduce a new DMA-device callback. In case
> if provided it gets called from the dma_get_slave_caps() method and is
> able to override the generic DMA-device capabilities.

I thought there is a pattern to return something, but it seems none.
So, I have nothing against it to return void.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

But consider one comment below.

> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> Cc: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
> Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: linux-mips@...r.kernel.org
> Cc: devicetree@...r.kernel.org
> 
> ---
> 
> Changelog v3:
> - This is a new patch created as a result of the discussion with Vinod and
>   Andy in the framework of DW DMA burst and LLP capabilities.
> ---
>  drivers/dma/dmaengine.c   | 3 +++
>  include/linux/dmaengine.h | 2 ++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index ad56ad58932c..edbb11d56cde 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -599,6 +599,9 @@ int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps)
>  	caps->cmd_resume = !!device->device_resume;
>  	caps->cmd_terminate = !!device->device_terminate_all;
>  

Perhaps a comment to explain that this is channel specific correction /
override / you name it on top of device level capabilities?

> +	if (device->device_caps)
> +		device->device_caps(chan, caps);
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(dma_get_slave_caps);
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index a7e4d8dfdd19..b303e59929e5 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -899,6 +899,8 @@ struct dma_device {
>  		struct dma_chan *chan, dma_addr_t dst, u64 data,
>  		unsigned long flags);
>  
> +	void (*device_caps)(struct dma_chan *chan,
> +			    struct dma_slave_caps *caps);
>  	int (*device_config)(struct dma_chan *chan,
>  			     struct dma_slave_config *config);
>  	int (*device_pause)(struct dma_chan *chan);
> -- 
> 2.26.2
> 

-- 
With Best Regards,
Andy Shevchenko