linux-kernel - Re: [PATCH v4 1/1] dmaengine: switchtec-dma: Introduce Switchtec DMA engine PCI driver

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Date:   Mon, 15 May 2023 22:00:56 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Kelvin.Cao@...rochip.com
Cc:     hch@...radead.org, dmaengine@...r.kernel.org, vkoul@...nel.org,
        George.Ge@...rochip.com, linux-kernel@...r.kernel.org,
        logang@...tatee.com, tglx@...utronix.de,
        christophe.jaillet@...adoo.fr
Subject: Re: [PATCH v4 1/1] dmaengine: switchtec-dma: Introduce Switchtec DMA
 engine PCI driver

On Mon, May 15, 2023 at 06:18:07PM +0000, Kelvin.Cao@...rochip.com wrote:
> > I find this rather confusing, especially as some code literally
> > switches on the op to fill in either set.
> 
> It's a hardware interface, and not possible to change it at the point.
> I guess I can make it look slightly better by grouping the related
> names together:
> 
> union {
>         struct {
>                 __le32 saddr_lo;
>                 __le32 saddr_hi;
>         };
>         struct {
>                 __le32 widata_lo;
>                 __le32 widata_hi;
>         };
> };

The hardware interface is simply:

	__le32 field_lo;
	__le32 field_hi;

hardware documentation might decide to give those fields two different
names just to confuse you :)

I think everyone else would be served better by:
	
	__le32 addr_lo; /* SADDR_LO/WIADDR_LO */
	__le32 addr_hi; /* SADDR_HI/WIADDR_HI */