Re: [RFC PATCH v3 2/6] swiotlb: Add restricted DMA pool

[Claire Chang <tientzu@xxxxxxxxxxxx>]

On Wed, Jan 13, 2021 at 8:42 PM Christoph Hellwig <hch@xxxxxx> wrote:
>
> > +#ifdef CONFIG_SWIOTLB
> > +     struct io_tlb_mem       *dma_io_tlb_mem;
> >  #endif
>
> Please add a new config option for this code instead of always building
> it when swiotlb is enabled.
>
> > +static int swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t 
> > start,
> > +                                size_t size)
>
> Can you split the refactoring in swiotlb.c into one or more prep
> patches?
>
> > +static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
> > +                                 struct device *dev)
> > +{
> > +     struct io_tlb_mem *mem = rmem->priv;
> > +     int ret;
> > +
> > +     if (dev->dma_io_tlb_mem)
> > +             return -EBUSY;
> > +
> > +     if (!mem) {
> > +             mem = kzalloc(sizeof(*mem), GFP_KERNEL);
> > +             if (!mem)
> > +                     return -ENOMEM;
>
> What is the calling convention here that allows for a NULL and non-NULL
> private data?

Since multiple devices can share the same pool, the private data,
io_tlb_mem struct, will be initialized by the first device attached to
it.
This is similar to rmem_dma_device_init() in kernel/dma/coherent.c.
I'll add a comment for it in next version.