Subject: Re: [PATCH kernel v10 23/34] powerpc/iommu/powernv: Release replaced TCE

From: Thomas Huth <[email-masked]>
Date: Fri, 15 May 2015 10:09:49 +0200

On Thu, 14 May 2015 13:53:57 +1000
Alexey Kardashevskiy <[email-masked]> wrote:

> On 05/14/2015 01:00 AM, Thomas Huth wrote:
> > On Tue, 12 May 2015 01:39:12 +1000
> > Alexey Kardashevskiy <[email-masked]> wrote:
...
> >> -/*
> >> - * hwaddr is a kernel virtual address here (0xc... bazillion),
> >> - * tce_build converts it to a physical address.
> >> - */
> >> -int iommu_tce_build(struct iommu_table *tbl, unsigned long entry,
> >> -		unsigned long hwaddr, enum dma_data_direction direction)
> >> -{
> >> -	int ret = -EBUSY;
> >> -	unsigned long oldtce;
> >> -	struct iommu_pool *pool = get_pool(tbl, entry);
> >> -
> >> -	spin_lock(&(pool->lock));
> >> -
> >> -	oldtce = tbl->it_ops->get(tbl, entry);
> >> -	/* Add new entry if it is not busy */
> >> -	if (!(oldtce & (TCE_PCI_WRITE | TCE_PCI_READ)))
> >> -		ret = tbl->it_ops->set(tbl, entry, 1, hwaddr, direction, NULL);
> >> -
> >> -	spin_unlock(&(pool->lock));
> >> +	if (!ret && ((*direction == DMA_FROM_DEVICE) ||
> >> +			(*direction == DMA_BIDIRECTIONAL)))
> >
> > You could drop some of the parentheses:
> >
> > 	if (!ret && (*direction == DMA_FROM_DEVICE ||
> > 			*direction == DMA_BIDIRECTIONAL))
> 
> I really (really) like braces. Is there any kernel code design rule against it?

I don't think so ... but for me it's rather the other way round: If I
see too many braces, I always wonder whether there is a reason for it in
the sense that I did not understand the statement right at the first
glance. Additionally, this is something that Pascal programmers like to
do, so IMHO this just looks ugly in C.

> >> @@ -405,19 +410,26 @@ static long tce_iommu_ioctl(void *iommu_data,
> >>   			return -EINVAL;
> >>
> >>   		/* iova is checked by the IOMMU API */
> >> -		tce = param.vaddr;
> >>   		if (param.flags & VFIO_DMA_MAP_FLAG_READ)
> >> -			tce |= TCE_PCI_READ;
> >> -		if (param.flags & VFIO_DMA_MAP_FLAG_WRITE)
> >> -			tce |= TCE_PCI_WRITE;
> >> +			if (param.flags & VFIO_DMA_MAP_FLAG_WRITE)
> >> +				direction = DMA_BIDIRECTIONAL;
> >> +			else
> >> +				direction = DMA_TO_DEVICE;
> >> +		else
> >> +			if (param.flags & VFIO_DMA_MAP_FLAG_WRITE)
> >> +				direction = DMA_FROM_DEVICE;
> >> +			else
> >> +				return -EINVAL;
> >
> > IMHO some curly braces for the outer if-statement would be really fine
> > here.
> 
> I believe checkpatch.pl won't like it. There is a check against single 
> lines having braces after "if" statements.

If you write your code like this (I was only talking about the outer
braces!):

	if (param.flags & VFIO_DMA_MAP_FLAG_READ) {
		if (param.flags & VFIO_DMA_MAP_FLAG_WRITE)
			direction = DMA_BIDIRECTIONAL;
		else
			direction = DMA_TO_DEVICE;
	} else {
		if (param.flags & VFIO_DMA_MAP_FLAG_WRITE)
			direction = DMA_FROM_DEVICE;
		else
			return -EINVAL;
	}

... then checkpatch should not complain, as far as I know - in this
case, the braces include three lines, don't they?

 Thomas