linux-kernel - Re: [PATCH 2/2] dmaengine: Add STM32 MDMA driver

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Date:   Mon, 1 May 2017 11:42:30 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Pierre Yves MORDRET <pierre-yves.mordret@...com>
Cc:     M'boumba Cedric Madianga <cedric.madianga@...il.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] dmaengine: Add STM32 MDMA driver

On Wed, Apr 26, 2017 at 12:35:46PM +0000, Pierre Yves MORDRET wrote:
> On 04/06/2017 09:08 AM, Vinod Koul wrote:
> >> +static int stm32_mdma_get_width(struct stm32_mdma_chan *chan,
> >> +				enum dma_slave_buswidth width)
> >> +{
> >> +	switch (width) {
> >> +	case DMA_SLAVE_BUSWIDTH_1_BYTE:
> >> +		return STM32_MDMA_BYTE;
> >> +	case DMA_SLAVE_BUSWIDTH_2_BYTES:
> >> +		return STM32_MDMA_HALF_WORD;
> >> +	case DMA_SLAVE_BUSWIDTH_4_BYTES:
> >> +		return STM32_MDMA_WORD;
> >> +	case DMA_SLAVE_BUSWIDTH_8_BYTES:
> >> +		return STM32_MDMA_DOUBLE_WORD;
> >
> > IIUC we can do this with ffs()
> 
> I don't believe we can do that. This function translates DMA_SLAVE enum 
> into internal register representation.

Yes and internal represenation seemed to be ffs() of dmanegine one.

> >> +subsys_initcall(stm32_mdma_init);
> >
> > why subsys?
> >
> 
> subsys_initcall level is to ensure MDMA is going to be probed before its 
> clients

Please use deffered probe approach for that

-- 
~Vinod