Re: [PATCH 0/6] RISC-V: Add eMMC support for TH1520 boards
From: Robin Murphy
Date: Wed Oct 04 2023 - 09:50:10 EST
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@xxxxxxxxxx> 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@xxxxxxxxx> wrote:
On Thu, Sep 21, 2023 at 8:51 PM Drew Fustini <dfustini@xxxxxxxxxxxx> 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@xxxxxxxxxx/
[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
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@xxxxxxxxxxxxxx/
[3] https://lore.kernel.org/linux-riscv/20230818135723.80612-6-prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx/
[4] https://gist.github.com/pdp7/91e72a663d3bb73eb28182337ad8bbcb