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Wed, 13 Jan 2021 09:43:21 -0800 (PST) Subject: Re: [RFC PATCH v3 2/6] swiotlb: Add restricted DMA pool To: Robin Murphy , Nicolas Saenz Julienne , Claire Chang , robh+dt@kernel.org, mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org, joro@8bytes.org, will@kernel.org, frowand.list@gmail.com, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com, jgross@suse.com, sstabellini@kernel.org, hch@lst.de, m.szyprowski@samsung.com Cc: drinkcat@chromium.org, devicetree@vger.kernel.org, heikki.krogerus@linux.intel.com, saravanak@google.com, peterz@infradead.org, xypron.glpk@gmx.de, rafael.j.wysocki@intel.com, linux-kernel@vger.kernel.org, andriy.shevchenko@linux.intel.com, bgolaszewski@baylibre.com, iommu@lists.linux-foundation.org, grant.likely@arm.com, rdunlap@infradead.org, gregkh@linuxfoundation.org, xen-devel@lists.xenproject.org, dan.j.williams@intel.com, treding@nvidia.com, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org References: <20210106034124.30560-1-tientzu@chromium.org> <20210106034124.30560-3-tientzu@chromium.org> <95ae9c1e-c1f1-5736-fe86-12ced1f648f9@gmail.com> <7ed51025f051f65f3dfe10a88caeb648821994b1.camel@suse.de> <4c4989b5-f825-7e04-ca66-038cf6b9d5e9@arm.com> From: Florian Fainelli Autocrypt: addr=f.fainelli@gmail.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <4c4989b5-f825-7e04-ca66-038cf6b9d5e9@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org 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 >>>> --- >>>>   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