Re: [PATCH 0/6] RISC-V: Add eMMC support for TH1520 boards

[Icenowy Zheng <uwu@icenowy.me>]

在 2023-10-04星期三的 14:49 +0100，Robin Murphy写道：
> On 04/10/2023 2:02 pm, Lad, Prabhakar wrote:
> > + CC linux-mm and Robin Murphy
> > 
> > On Wed, Oct 4, 2023 at 12:42 PM Jisheng Zhang <jszhang@kernel.org>
> > wrote:
> > > 
> > > On Mon, Oct 02, 2023 at 09:37:44PM -0700, Drew Fustini wrote:
> > > > On Fri, Sep 22, 2023 at 05:48:21PM -0500, Robert Nelson wrote:
> > > > > On Fri, Sep 22, 2023 at 2:08 PM Robert Nelson
> > > > > <robertcnelson@gmail.com> wrote:
> > > > > > 
> > > > > > On Thu, Sep 21, 2023 at 8:51 PM Drew Fustini
> > > > > > <dfustini@baylibre.com> wrote:
> > > > > > > 
> > > > > > > This series adds support for the eMMC on the BeagleV
> > > > > > > Ahead and the
> > > > > > > Sipeed LicheePi 4A. This allows the kernel to boot with
> > > > > > > the rootfs on
> > > > > > > eMMC.
> > > > > > > 
> > > > > > > I tested on top of v6.6-rc2 with this config [1]. I was
> > > > > > > able to boot
> > > > > > > both the Ahead [2] and LPi4a [3] from eMMC. The following
> > > > > > > prerequisites
> > > > > > > are required:
> > > > > > > 
> > > > > > >    [PATCH v2] riscv: dts: thead: set dma-noncoherent to
> > > > > > > soc bus [4]
> > > > > > > 
> > > > > > > I pushed a branch [5] with this patch series and the
> > > > > > > above patch for
> > > > > > > those that find a git branch easier to test.
> > > > > > > 
> > > > > > > Please note that only the MMC controller connected to the
> > > > > > > eMMC device
> > > > > > > is enabled in the device trees for these two boards. I
> > > > > > > did not yet
> > > > > > > attempt to configure and use the microSD card slot. My
> > > > > > > preference is to
> > > > > > > address that in a future patch series.
> > > > > > > 
> > > > > > > References:
> > > > > > > [1]
> > > > > > > https://gist.github.com/pdp7/5fbdcf2a65eb1abdd3a29d519c19cdd2
> > > > > > > [2]
> > > > > > > https://gist.github.com/pdp7/91a801a5f8d1070c53509eda9800ad78
> > > > > > > [3]
> > > > > > > https://gist.github.com/pdp7/1445c3c991e88fd69c60165cef65726a
> > > > > > > [4]
> > > > > > > https://lore.kernel.org/linux-riscv/20230912072232.2455-1-jszhang@kernel.org/
> > > > > > > [5] https://github.com/pdp7/linux/tree/b4/th1520-mmc
> > > > > > 
> > > > > > This patchset came out very nice!
> > > > > > 
> > > > > > v6.6-rc2 with Last RFC v2:
> > > > > > 
> > > > > > [    4.066630] mmc0: SDHCI controller on ffe7080000.mmc
> > > > > > [ffe7080000.mmc] using PIO
> > > > > > 
> > > > > > debian@BeagleV:~$ sudo hdparm -tT /dev/mmcblk0
> > > > > > 
> > > > > > /dev/mmcblk0:
> > > > > >   Timing cached reads:   1516 MB in  2.00 seconds = 758.09
> > > > > > MB/sec
> > > > > >   Timing buffered disk reads:  84 MB in  3.01 seconds = 
> > > > > > 27.94 MB/sec
> > > > > > 
> > > > > > vs v6.6-rc2 with this patchset:
> > > > > > 
> > > > > >   [    4.096837] mmc0: SDHCI controller on ffe7080000.mmc
> > > > > > [ffe7080000.mmc] using DMA
> > > > > > 
> > > > > > debian@BeagleV:~$ sudo hdparm -tT /dev/mmcblk0
> > > > > > 
> > > > > > /dev/mmcblk0:
> > > > > >   Timing cached reads:   1580 MB in  2.00 seconds = 790.97
> > > > > > MB/sec
> > > > > >   Timing buffered disk reads: 418 MB in  3.00 seconds =
> > > > > > 139.11 MB/sec
> > > > > 
> > > > > Drew pointed out on Slack, this was not quite right.. After
> > > > > more
> > > > > digging by Drew, CONFIG_DMA_GLOBAL_POOL is causing a DMA
> > > > > limitation
> > > > > with the multiplatform defconfig. so with,
> > > > > 
> > > > > ./scripts/config --disable CONFIG_ARCH_R9A07G043
> > > > > 
> > > > > (to remove CONFIG_DMA_GLOBAL_POOL)... another 2x in buffered
> > > > > reads..
> > > > > 
> > > > > [    4.059242] mmc0: SDHCI controller on ffe7080000.mmc
> > > > > [ffe7080000.mmc] using ADMA 64-bit
> > > > > 
> > > > > debian@BeagleV:~$ sudo hdparm -tT /dev/mmcblk0
> > > > > 
> > > > > /dev/mmcblk0:
> > > > >   Timing cached reads:   1600 MB in  2.00 seconds = 800.93
> > > > > MB/sec
> > > > >   Timing buffered disk reads: 892 MB in  3.00 seconds =
> > > > > 297.06 MB/sec
> > > > 
> > > > It seems CONFIG_DMA_GLOBAL_POOL=y causes ADMA buffer alloc to
> > > > fail [1]:
> > > > 
> > > >    mmc0: Unable to allocate ADMA buffers - falling back to
> > > > standard DMA
> > > > 
> > > > Prabhakar's AX45MP non-coherent DMA support [2] series
> > > > introduced the
> > > > selection of DMA_GLOBAL_POOL for ARCH_R9A07G043 and the riscv
> > > > defconfig
> > > > selects ARCH_R9A07G043.
> > > > 
> > > > Patch 5 in the series [3] states that:
> > > > 
> > > >    With DMA_GLOBAL_POOL enabled all DMA allocations happen from
> > > > this
> > > >    region and synchronization callbacks are implemented to
> > > > synchronize
> > > >    when doing DMA transactions.
> > > > 
> > > > This example of a "shared-dma-pool" node was given:
> > > > 
> > > >          pma_resv0@58000000 {
> > > >              compatible = "shared-dma-pool";
> > > >              reg = <0x0 0x58000000 0x0 0x08000000>;
> > > >              no-map;
> > > >              linux,dma-default;
> > > >          };
> > > > 
> > > > I've copied that to th1520-beaglev-ahead.dts. The address of
> > > > 0x58000000
> > > > has no significance on th1520, but the existence of shared-dma-
> > > > pool
> > > > seems to fix the problem. ADMA mode [4] is now working even
> > > > though
> > > > CONFIG_DMA_GLOBAL_POOL=y.
> > > 
> > > + Christoph, Lad
> > > 
> > > IMHO, this is not TH1520 specific but a generic issue.
> > > 
> > > I believe commit 484861e09f3e ("soc: renesas: Kconfig: Select the
> > > required configs for RZ/Five SoC") can cause regression on all
> > > non-dma-coherent riscv platforms with generic defconfig. This is
> > > a common issue. The logic here is: generic riscv defconfig
> > > selects
> > > ARCH_R9A07G043 which selects DMA_GLOBAL_POOL, which assumes all
> > > non-dma-coherent riscv platforms have a dma global pool, this
> > > assumption
> > > seems not correct. And I believe DMA_GLOBAL_POOL should not be
> > > selected by ARCH_SOCFAMILIY, instead, only ARCH under some
> > > specific
> > > conditions can select it globaly, for example NOMMU ARM and so
> > > on.
> > > 
> > > Since this is a regression, what's proper fix? any suggestion is
> > > appreciated.
> 
> I think the answer is to not select DMA_GLOBAL_POOL, since that is
> only 

Well I think for RISC-V, it's not NOMMU only but applicable for every
core that does not support Svpbmt or vendor-specific alternatives,
because the original RISC-V priv spec does not define memory attributes
in page table entries.

For the Renesas/Andes case I think a pool is set by OpenSBI with
vendor-specific M-mode facility and then passed in DT, and the S-mode
(which MMU is enabled in) just sees fixed memory attributes, in this
case I think DMA_GLOBAL_POOL is needed.

> designed for nommu cases where non-cacheable memory lives in a fixed 
> place in the physical address map, and regular kernel pages can't be 
> remapped. As far as I'm aware, RISCV_DMA_NONCOHERENT is the thing you
> want, such that DMA_DIRECT_REMAP can dynamically provide non-
> cacheable 
> coherent buffers for non-hardware-coherent devices.
> 
> Thanks,
> Robin.
> 
> > > 
> > > Thanks
> > > 
> > > > 
> > > > Thanks,
> > > > Drew
> > > > 
> > > > [1]
> > > > https://gist.github.com/pdp7/73041ed808bbc7dd445836fb90574979
> > > > [2]
> > > > https://lore.kernel.org/linux-riscv/20230818135723.80612-1-prabhakar.mahadev-lad.rj@bp.renesas.com/
> > > > [3]
> > > > https://lore.kernel.org/linux-riscv/20230818135723.80612-6-prabhakar.mahadev-lad.rj@bp.renesas.com/
> > > > [4]
> > > > https://gist.github.com/pdp7/91e72a663d3bb73eb28182337ad8bbcb