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

From: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
To: Vinod <vkoul@kernel.org>
Cc: dan.j.williams@intel.com, afaerber@suse.de, robh+dt@kernel.org,
	gregkh@linuxfoundation.org, jslaby@suse.com,
	linux-serial@vger.kernel.org, dmaengine@vger.kernel.org,
	liuwei@actions-semi.com, 96boards@ucrobotics.com,
	devicetree@vger.kernel.org, daniel.thompson@linaro.org,
	amit.kucheria@linaro.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, hzhang@ucrobotics.com,
	bdong@ucrobotics.com, manivannanece23@gmail.com,
	thomas.liau@actions-semi.com, jeff.chen@actions-semi.com,
	pn@denx.de, edgar.righi@lsitec.org.br
Subject: Re: [PATCH 2/3] dmaengine: Add Slave and Cyclic mode support for Actions Semi Owl S900 SoC
Date: Tue, 18 Sep 2018 16:56:29 -0700	[thread overview]
Message-ID: <20180918235629.GA20199@Mani-XPS-13-9360> (raw)
In-Reply-To: <20180918233414.GA19844@Mani-XPS-13-9360>

On Tue, Sep 18, 2018 at 04:34:14PM -0700, Manivannan Sadhasivam wrote:
> 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?
>

I think it is better to select 32bit mode eventhough it is the default one.
Will update it in next revision.

Thanks,
Mani

> Thanks,
> Mani
> 
> > -- 
> > ~Vinod