On 1/13/21 7:27 AM, Robin Murphy wrote:
> On 2021-01-13 13:59, Nicolas Saenz Julienne wrote:
>> 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 <tien...@chromium.org>
>>>> ---
>>>> 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.
>
> TBH I really don't think this needs calling out at all. Even in the
> regular case, the details of exactly how and where the pool is allocated
> are beyond the scope of this code - architectures already have several
> ways to control that and make their own decisions.
>
>>>
>>> [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?
>
> More than that, I'd assume that we *have* to use the linear/direct map
> address rather than anything that has any possibility of being a vmalloc
> remap, otherwise we can no longer safely rely on
> phys_to_dma/dma_to_phys, no?
I believe you are right, which means that if we want to make use of the
restricted DMA pool on a 32-bit architecture (and we do, at least, I do)
we should probably add some error checking/warning to ensure the
restricted DMA pool falls within the linear map.
--
Florian
