Re: [PATCH v4 07/11] dmaengine: dw: Set DMA device max segment size parameter

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Fri, May 29, 2020 at 01:23:57AM +0300, Serge Semin wrote:
> Maximum block size DW DMAC configuration corresponds to the max segment
> size DMA parameter in the DMA core subsystem notation. Lets set it with a
> value specific to the probed DW DMA controller. It shall help the DMA
> clients to create size-optimized SG-list items for the controller. This in
> turn will cause less dw_desc allocations, less LLP reinitializations,
> better DMA device performance.

Yes, something like that for time being, thanks!

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

> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: linux-mips@vger.kernel.org
> Cc: devicetree@vger.kernel.org
> 
> ---
> 
> Changelog v2:
> - This is a new patch created in place of the dropped one:
>   "dmaengine: dw: Add LLP and block size config accessors".
> 
> Changelog v3:
> - Use the block_size found for the very first channel instead of looking for
>   the maximum of maximum block sizes.
> - Don't define device-specific device_dma_parameters object, since it has
>   already been defined by the platform device core.
> ---
>  drivers/dma/dw/core.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
> index 33e99d95b3d3..fb95920c429e 100644
> --- a/drivers/dma/dw/core.c
> +++ b/drivers/dma/dw/core.c
> @@ -1229,6 +1229,13 @@ int do_dma_probe(struct dw_dma_chip *chip)
>  			     BIT(DMA_MEM_TO_MEM);
>  	dw->dma.residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
>  
> +	/*
> +	 * For now there is no hardware with non uniform maximum block size
> +	 * across all of the device channels, so we set the maximum segment
> +	 * size as the block size found for the very first channel.
> +	 */
> +	dma_set_max_seg_size(dw->dma.dev, dw->chan[0].block_size);
> +
>  	err = dma_async_device_register(&dw->dma);
>  	if (err)
>  		goto err_dma_register;
> -- 
> 2.26.2
> 

-- 
With Best Regards,
Andy Shevchenko