linux-kernel - Re: [PATCH v1 1/3] dmaengine: Add support for APM X-Gene SoC DMA driver

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Message-ID: <CAFd313zXsoWjDVEKSQpMKMxuP7U8oRmo=sEo8P3iHysDnJDvsg@mail.gmail.com>
Date:	Fri, 2 Jan 2015 14:35:43 +0530
From:	Rameshwar Sahu <rsahu@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org, vinod.koul@...el.com,
	dan.j.williams@...el.com, devicetree@...r.kernel.org,
	Jon Masters <jcm@...hat.com>, patches@....com,
	linux-kernel@...r.kernel.org, Don Dutile <ddutile@...hat.com>,
	Loc Ho <lho@....com>, dmaengine@...r.kernel.org
Subject: Re: [PATCH v1 1/3] dmaengine: Add support for APM X-Gene SoC DMA driver

Hi Arnd,

See inline...

Thanks,
with regards,
Ram


On Wed, Dec 31, 2014 at 8:21 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Wednesday 31 December 2014 17:12:14 Rameshwar Prasad Sahu wrote:
>> This patch implements the APM X-Gene SoC DMA driver. The APM X-Gene
>> SoC DMA engine consists of 4 DMA channels for performing DMA operations.
>> These DMA operations include memory copy and scatter gathering offload.
>
> Is the dma engine capable of slave DMA in theory and you just don't use
> that, or does it not do that at all?

This DMA engine is not capable of slave DMA.


>
>> +static int xgene_dma_init_mem(struct xgene_dma *pdma)
>> +{
>> +     int timeout = 1000;
>> +
>> +     writel(0x0, pdma->csr_dma + DMA_MEM_RAM_SHUTDOWN);
>> +
>> +     /* Force a barrier */
>> +     readl(pdma->csr_dma + DMA_MEM_RAM_SHUTDOWN);
>> +
>> +     do {
>> +             if (readl(pdma->csr_dma + DMA_BLK_MEM_RDY)
>> +                     == DMA_BLK_MEM_RDY_DEFAULT)
>> +                     break;
>> +             udelay(1);
>> +     } while (--timeout);
>> +
>> +     if (timeout <= 0) {
>> +             dev_err(pdma->dev,
>> +                     "Failed to release memory from shutdown\n");
>> +             return -ENODEV;
>> +     }
>> +     return 0;
>> +}
>
> That's a long busy-loop. Can you use a sleeping function instead?

Okay I will do this.

>
>> +     /* Set DMA mask and coherent mask */
>> +     ret = dma_coerce_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
>> +     if (ret) {
>> +             dev_err(&pdev->dev, "Failed to set DMA mask\n");
>> +             goto err_pm_enable;
>> +     }
>
> Never use dma_coerce_mask_and_coherent in new drivers. Instead, make
> sure that the information in the device tree is correct in the first
> place so the driver doesn't need to override it.
>
>         Arnd
>

Okay I will use function for DMA masking that other driver uses.
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