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

[Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>]

Hi All,

On Tue, 2021-01-12 at 16:03 -0800, Florian Fainelli wrote:
> On 1/5/21 7:41 PM, Claire Chang wrote:
> > Add the initialization function to create restricted DMA pools from
> > matching reserved-memory nodes in the device tree.
> > 
> > Signed-off-by: Claire Chang <tientzu@xxxxxxxxxxxx>
> > ---
> >  include/linux/device.h  |   4 ++
> >  include/linux/swiotlb.h |   7 +-
> >  kernel/dma/Kconfig      |   1 +
> >  kernel/dma/swiotlb.c    | 144 ++++++++++++++++++++++++++++++++++------
> >  4 files changed, 131 insertions(+), 25 deletions(-)
> > 
> > diff --git a/include/linux/device.h b/include/linux/device.h
> > index 89bb8b84173e..ca6f71ec8871 100644
> > --- a/include/linux/device.h
> > +++ b/include/linux/device.h
> > @@ -413,6 +413,7 @@ struct dev_links_info {
> >   * @dma_pools:     Dma pools (if dma'ble device).
> >   * @dma_mem:       Internal for coherent mem override.
> >   * @cma_area:      Contiguous memory area for dma allocations
> > + * @dma_io_tlb_mem: Internal for swiotlb io_tlb_mem override.
> >   * @archdata:      For arch-specific additions.
> >   * @of_node:       Associated device tree node.
> >   * @fwnode:        Associated device node supplied by platform firmware.
> > @@ -515,6 +516,9 @@ struct device {
> >  #ifdef CONFIG_DMA_CMA
> >     struct cma *cma_area;           /* contiguous memory area for dma
> >                                        allocations */
> > +#endif
> > +#ifdef CONFIG_SWIOTLB
> > +   struct io_tlb_mem       *dma_io_tlb_mem;
> >  #endif
> >     /* arch specific additions */
> >     struct dev_archdata     archdata;
> > diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> > index dd8eb57cbb8f..a1bbd7788885 100644
> > --- a/include/linux/swiotlb.h
> > +++ b/include/linux/swiotlb.h
> > @@ -76,12 +76,13 @@ extern enum swiotlb_force swiotlb_force;
> >   *
> >   * @start: The start address of the swiotlb memory pool. Used to do a quick
> >   *         range check to see if the memory was in fact allocated by this
> > - *         API.
> > + *         API. For restricted DMA pool, this is device tree adjustable.
> 
> Maybe write it as this is "firmware adjustable" such that when/if ACPI
> needs something like this, the description does not need updating.
> 
> [snip]
> 
> > +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;
> > +
> > +           if (!memremap(rmem->base, rmem->size, MEMREMAP_WB)) {
> 
> MEMREMAP_WB sounds appropriate as a default.

As per the binding 'no-map' has to be disabled here. So AFAIU, this memory will
be part of the linear mapping. Is this really needed then?

> Documentation/devicetree/bindings/reserved-memory/ramoops.txt does
> define an "unbuffered" property which in premise could be applied to the
> generic reserved memory binding as well and that we may have to be
> honoring here, if we were to make it more generic. Oh well, this does
> not need to be addressed right now I guess.

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