From: Atish Patra <atishp@atishpatra.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Atish Patra <atish.patra@wdc.com>,
devicetree <devicetree@vger.kernel.org>,
Albert Ou <aou@eecs.berkeley.edu>,
Tobias Klauser <tklauser@distanz.ch>,
Robin Murphy <robin.murphy@arm.com>,
"linux-kernel@vger.kernel.org List"
<linux-kernel@vger.kernel.org>, Rob Herring <robh+dt@kernel.org>,
iommu@lists.linux-foundation.org,
Guo Ren <guoren@linux.alibaba.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
linux-riscv <linux-riscv@lists.infradead.org>,
Frank Rowand <frowand.list@gmail.com>,
Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [RFC 3/5] dma-mapping: Enable global non-coherent pool support for RISC-V
Date: Mon, 26 Jul 2021 15:47:54 -0700 [thread overview]
Message-ID: <CAOnJCU+qRznBTn9Mt6t_DE6UUz6_LuaBBuOmnURS2Yh3pmpjvg@mail.gmail.com> (raw)
In-Reply-To: <20210726070030.GB9035@lst.de>
On Mon, Jul 26, 2021 at 12:00 AM Christoph Hellwig <hch@lst.de> wrote:
>
> On Fri, Jul 23, 2021 at 02:40:29PM -0700, Atish Patra wrote:
> > Currently, linux,dma-default is used to reserve a global non-coherent pool
> > to allocate memory for dma operations. This can be useful for RISC-V as
> > well as the ISA specification doesn't specify a method to modify PMA
> > attributes or page table entries to define non-cacheable area yet.
> > A non-cacheable memory window is an alternate options for vendors to
> > support non-coherent devices.
>
> Please explain why you do not want to use the simply non-cachable
> window support using arch_dma_set_uncached as used by mips, niops2 and
> xtensa.
>
arch_dma_set_uncached works as well in this case. However, mips,
niops2 & xtensa uses a
fixed (via config) value for the offset. Similar approach can't be
used here because the platform specific
offset value has to be determined at runtime so that a single kernel
image can boot on all platforms.
That's why we need the following additional changes for RISC-V to make it work.
1. a new DT property so that arch specific code is aware of the
non-cacheable window offset.
- either under /chosen node or a completely separate node with
multiple non-cacheable window support
We also need to define how it is going to referenced from
individual device if a per-device non-cacheable
window support is required in future. As of now, the beagleV memory
region lies in 0x10_0000_00000 - x17_FFFF_FFFF
which is mapped to start of DRAM 0x80000000. All of the
non-coherent devices can do 32bit DMA only.
2. Use the dma-ranges and modify the arch_dma_set_uncached function to
pass the struct device as an argument.
Either way, we will need arch specific hook ups and additional changes
while the global non-coherent pool
provides a more elegant solution without any additional arch specific code.
If arch_dma_set_uncached is still preferred way to solve this problem,
I can revise the patch with either approach 1 or approach 2
> > +static int __dma_init_global_coherent(phys_addr_t phys_addr, dma_addr_t device_addr, size_t size)
>
>
>
>
> > {
> > struct dma_coherent_mem *mem;
> >
> > - mem = dma_init_coherent_memory(phys_addr, phys_addr, size, true);
> > + if (phys_addr == device_addr)
> > + mem = dma_init_coherent_memory(phys_addr, device_addr, size, true);
> > + else
> > + mem = dma_init_coherent_memory(phys_addr, device_addr, size, false);
>
> Nak. The phys_addr != device_addr support is goign away. This needs
ok.
> to be filled in using dma-ranges property hanging of the struct device.
struct device is only accessible in rmem_dma_device_init. I couldn't
find a proper way to access it during
dma_reserved_default_memory setup under global pool.
Does that mean we should use a per-device memory pool instead of a
global non-coherent pool ?
> _______________________________________________
> iommu mailing list
> iommu@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
--
Regards,
Atish
next prev parent reply other threads:[~2021-07-26 22:48 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-23 21:40 [RFC 0/5] Support non-coherent DMA on RISC-V using a global pool Atish Patra
2021-07-23 21:40 ` [RFC 1/5] RISC-V: Implement arch_sync_dma* functions Atish Patra
2021-07-26 6:56 ` Christoph Hellwig
2021-07-26 21:52 ` Atish Patra
2021-09-11 9:37 ` Guo Ren
2021-08-17 1:48 ` Guo Ren
2021-08-17 3:24 ` Atish Patra
2021-08-17 6:28 ` Guo Ren
2021-07-23 21:40 ` [RFC 2/5] of: Move of_dma_get_range to of_address.h Atish Patra
2021-07-23 21:40 ` [RFC 3/5] dma-mapping: Enable global non-coherent pool support for RISC-V Atish Patra
2021-07-25 22:29 ` Rob Herring
2021-07-26 7:00 ` Christoph Hellwig
2021-07-26 22:47 ` Atish Patra [this message]
2021-07-27 8:52 ` Christoph Hellwig
2021-08-02 18:22 ` Atish Patra
2021-07-23 21:40 ` [RFC 4/5] dma-direct: Allocate dma pages directly if global pool allocation fails Atish Patra
2021-07-26 7:01 ` Christoph Hellwig
2021-07-23 21:40 ` [RFC 5/5] RISC-V: Support a new config option for non-coherent DMA Atish Patra
2021-07-29 4:30 ` [RFC 0/5] Support non-coherent DMA on RISC-V using a global pool Palmer Dabbelt
2021-07-29 6:19 ` Atish Patra
2021-08-17 1:37 ` Guo Ren
2021-08-17 3:28 ` Atish Patra
2021-08-17 6:42 ` Guo Ren
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