linux-kernel - Re: [PATCH v4 09/11] dmaengine: dw: Initialize min

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Date:   Fri, 29 May 2020 13:25:15 +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 09/11] dmaengine: dw: Initialize min_burst capability

On Fri, May 29, 2020 at 01:23:59AM +0300, Serge Semin wrote:
> According to the DW APB DMAC data book the minimum burst transaction
> length is 1 and it's true for any version of the controller since
> isn't parametrised in the coreAssembler so can't be changed at the
> IP-core synthesis stage. Let's initialise the min_burst member of the
> DMA controller descriptor so the DMA clients could use it to properly
> optimize the DMA requests.

> @@ -1229,6 +1229,7 @@ int do_dma_probe(struct dw_dma_chip *chip)
>  	dw->dma.device_issue_pending = dwc_issue_pending;
>  
>  	/* DMA capabilities */

> +	dw->dma.min_burst = 1;

Perhaps then relaxed maximum, like

	dw->dma.max_burst = 256;

(channels will update this)

?

>  	dw->dma.src_addr_widths = DW_DMA_BUSWIDTHS;
>  	dw->dma.dst_addr_widths = DW_DMA_BUSWIDTHS;
>  	dw->dma.directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV) |
> -- 
> 2.26.2
> 

-- 
With Best Regards,
Andy Shevchenko