linux-kernel - Re: [PATCH 2/3] dmaengine: Add Slave and Cyclic mode support for Actions Semi Owl S900 SoC

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Date:   Tue, 18 Sep 2018 16:34:14 -0700
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Vinod <vkoul@...nel.org>
Cc:     dan.j.williams@...el.com, afaerber@...e.de, robh+dt@...nel.org,
        gregkh@...uxfoundation.org, jslaby@...e.com,
        linux-serial@...r.kernel.org, dmaengine@...r.kernel.org,
        liuwei@...ions-semi.com, 96boards@...obotics.com,
        devicetree@...r.kernel.org, daniel.thompson@...aro.org,
        amit.kucheria@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, hzhang@...obotics.com,
        bdong@...obotics.com, manivannanece23@...il.com,
        thomas.liau@...ions-semi.com, jeff.chen@...ions-semi.com,
        pn@...x.de, edgar.righi@...tec.org.br
Subject: Re: [PATCH 2/3] dmaengine: Add Slave and Cyclic mode support for
 Actions Semi Owl S900 SoC

On Tue, Sep 18, 2018 at 04:32:00PM -0700, Vinod wrote:
> Hi Mani,
> 
> On 18-09-18, 15:52, Manivannan Sadhasivam wrote:
> > On Tue, Sep 18, 2018 at 09:35:12AM -0700, Vinod wrote:
> > > On 01-09-18, 22:12, Manivannan Sadhasivam wrote:
> > > 
> > > > @@ -364,6 +372,26 @@ static inline int owl_dma_cfg_lli(struct owl_dma_vchan *vchan,
> > > >  			OWL_DMA_MODE_DT_DCU | OWL_DMA_MODE_SAM_INC |
> > > >  			OWL_DMA_MODE_DAM_INC;
> > > >  
> > > > +		break;
> > > > +	case DMA_MEM_TO_DEV:
> > > > +		mode |= OWL_DMA_MODE_TS(vchan->drq)
> > > > +			| OWL_DMA_MODE_ST_DCU | OWL_DMA_MODE_DT_DEV
> > > > +			| OWL_DMA_MODE_SAM_INC | OWL_DMA_MODE_DAM_CONST;
> > > > +
> > > > +		/* Handle bus width for UART */
> > > > +		if (sconfig->dst_addr_width == DMA_SLAVE_BUSWIDTH_1_BYTE)
> > > > +			mode |= OWL_DMA_MODE_NDDBW_8BIT;
> > > 
> > > this is fine per se, but not correct way to handle in dmaengine driver.
> > > You should be agnostic to user of dmaengine, so handle all the buswidths
> > > the IP block supports and update the values accordingly. That way new
> > > uses can be added w/o requiring change in dmaengine driver
> > 
> > Currently, all members of Owl family supports only 32bit and 8bit
> > bus widths. 32bit is common for all peripherals and 8bit applies to only
> > UART since the internal buffer is 8bit wide. So, this makes sense to me!
> 
> Above you are onky handing DMA_SLAVE_BUSWIDTH_1_BYTE and not 32bit which
> this IP supports.. You should handle all widths supported vt hardware..
>

Hi Vinod,

Default width is 32bit and we will only override it for UART... Should I
add a comment stating this?

Thanks,
Mani

> -- 
> ~Vinod