From: Yixun Lan <dlan@kernel.org>
To: Vlad Banea <montrealtango@gmail.com>
Cc: troy.mitchell@linux.spacemit.com, wangruikang@iscas.ac.cn,
guodong.xu@oss.qualcomm.com, jyc0019@gmail.com, robh@kernel.org,
krzk+dt@kernel.org, conor+dt@kernel.org, pjw@kernel.org,
palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr,
devicetree@vger.kernel.org, linux-riscv@lists.infradead.org,
spacemit@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] riscv: dts: spacemit: k1: give each PCIe port its own DMA window
Date: Sat, 14 Nov 2026 01:44:14 +0000 [thread overview]
Message-ID: <20261114014414-GKA99639@kernel.org> (raw)
In-Reply-To: <20261113023158.2872492-1-montrealtango@gmail.com>
Hi Vlad Banea,
On 21:31 Thu 12 Nov , Vlad Banea wrote:
> On K1 a PCIe master only sees DDR: bus addresses 0-2 GB map to CPU
> 0-2 GB and bus 2-16 GB to CPU 4-18 GB. A root port does not forward
> upstream an inbound access that falls inside its own memory window, so
> dma-ranges must skip each port's own outbound window; the other ports'
> windows reach memory.
>
> The shared pcie-bus skips all three windows, bus 0x8000_0000-0xb7ff_ffff,
> which leaves CPU addresses 0x1_0000_0000-0x1_37ff_ffff unreachable from
> every port. Give each port its own bus that skips only its own window.
> On boards with more than 2 GB of RAM, each port can then reach another
> 512-640 MB without SWIOTLB bouncing.
>
> Signed-off-by: Vlad Banea <montrealtango@gmail.com>
> ---
>
> Notes:
> Changes in v2:
> - describe the K1 PCIe address map instead of citing the vendor DT (Troy)
> - "more than 2 GB" instead of 4 GB (Troy)
> - drop the RFC tag
> - RFC: https://lore.kernel.org/all/20261112015148.3911178-1-montrealtango@gmail.com/
>
> Tested on an OrangePi R2S (8 GB, RTL8125B on pcie1 and pcie2): SWIOTLB
> use under load went from up to 87 slots to none.
>
> arch/riscv/boot/dts/spacemit/k1.dtsi | 27 +++++++++++++++++++++++++--
> 1 file changed, 25 insertions(+), 2 deletions(-)
>
Reviewed-by: Yixun Lan <dlan@kernel.org>
--
Yixun Lan (dlan)
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prev parent reply other threads:[~2026-11-14 1:44 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-13 2:31 [PATCH v2] riscv: dts: spacemit: k1: give each PCIe port its own DMA window Vlad Banea
2026-11-13 8:40 ` Troy Mitchell
2026-11-14 1:44 ` Yixun Lan [this message]
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