linux-kernel - Re: [PATCH 3/4] dmaengine: dw: Simplify prepare CTL

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Date: Fri, 19 Apr 2024 00:00:40 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Serge Semin <fancer.lancer@...il.com>
Cc: Viresh Kumar <vireshk@...nel.org>, Vinod Koul <vkoul@...nel.org>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>, dmaengine@...r.kernel.org,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] dmaengine: dw: Simplify prepare CTL_LO methods

On Thu, Apr 18, 2024 at 10:00:02PM +0300, Serge Semin wrote:
> On Thu, Apr 18, 2024 at 02:47:18PM +0300, Andy Shevchenko wrote:
> > On Wed, Apr 17, 2024 at 11:11:46PM +0300, Serge Semin wrote:
> > > On Tue, Apr 16, 2024 at 10:04:42PM +0300, Andy Shevchenko wrote:
> > > > On Tue, Apr 16, 2024 at 07:28:57PM +0300, Serge Semin wrote:

..

> > > > > +	if (dwc->direction == DMA_MEM_TO_DEV) {
> > > > > +		sms = dwc->dws.m_master;
> > > > > +		smsize = 0;
> > > > > +		dms = dwc->dws.p_master;
> > > > > +		dmsize = sconfig->dst_maxburst;
> > > 
> > > > I would group it differently, i.e.
> > > > 
> > > > 		sms = dwc->dws.m_master;
> > > > 		dms = dwc->dws.p_master;
> > > > 		smsize = 0;
> > > > 		dmsize = sconfig->dst_maxburst;
> > > 
> > > Could you please clarify, why? From my point of view it was better to
> > > group the source master ID and the source master burst size inits
> > > together.
> 
> > Sure. The point here is that when you look at the DMA channel configuration
> > usually you operate with the semantically tied fields for source and
> > destination. At least this is my experience, I always check both sides
> > of the transfer for the same field, e.g., master setting, hence I want to
> > have them coupled.
> 
> Ok. I see. Thanks for clarification. I normally do that in another
> order: group the functionally related fields together - all
> source-related configs first, then all destination-related configs.
> Honestly I don't have strong opinion about this part, it's just my
> personal preference. Am I right to think that from your experience in
> kernel it's normally done in the order you described?

In this driver I believe I have followed that one, yes.

> > > > > +	} else if (dwc->direction == DMA_DEV_TO_MEM) {
> > > > > +		sms = dwc->dws.p_master;
> > > > > +		smsize = sconfig->src_maxburst;
> > > > > +		dms = dwc->dws.m_master;
> > > > > +		dmsize = 0;
> > > > > +	} else /* DMA_MEM_TO_MEM */ {
> > > > > +		sms = dwc->dws.m_master;
> > > > > +		smsize = 0;
> > > > > +		dms = dwc->dws.m_master;
> > > > > +		dmsize = 0;
> > > > > +	}
> > > > 
> > > > Ditto for two above cases.

-- 
With Best Regards,
Andy Shevchenko