linux-kernel - Re: [PATCH v2] ARM: dts: dra7: Add bus_dma

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Message-ID: <fb916d06-1521-25a5-2eae-94244a3f9d06@arm.com>
Date:   Fri, 13 Mar 2020 15:05:33 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Roger Quadros <rogerq@...com>, tony@...mide.com
Cc:     hch@....de, robh+dt@...nel.org, nm@...com, t-kristo@...com,
        nsekhar@...com, linux-omap@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...nel.org
Subject: Re: [PATCH v2] ARM: dts: dra7: Add bus_dma_limit for L3 bus

On 2020-03-13 9:47 am, Roger Quadros wrote:
> The L3 interconnect's memory map is from 0x0 to
> 0xffffffff. Out of this, System memory (SDRAM) can be
> accessed from 0x80000000 to 0xffffffff (2GB)
> 
> DRA7 does support 4GB of SDRAM but upper 2GB can only be
> accessed by the MPU subsystem.
> 
> Add the dma-ranges property to reflect the physical address limit
> of the L3 bus.
> 
> Issues ere observed only with SATA on DRA7-EVM with 4GB RAM
> and CONFIG_ARM_LPAE enabled. This is because the controller
> supports 64-bit DMA and its driver sets the dma_mask to 64-bit
> thus resulting in DMA accesses beyond L3 limit of 2G.
> 
> Setting the correct bus_dma_limit fixes the issue.

Neat! In principle you should no longer need the specific dma-ranges on 
the PCIe nodes, since AIUI those really only represent a subset of this 
general limitation, but given the other inheritance issue you saw it's 
probably safer to leave them as-is for now.

FWIW,

Reviewed-by: Robin Murphy <robin.murphy@....com>

> Signed-off-by: Roger Quadros <rogerq@...com>
> Cc: stable@...nel.org
> ---
> 
> Changelog:
> v2:
> - Revised patch with minimal intrusion. i.e. don't change #size-cells
>    of device node.
> 
>   arch/arm/boot/dts/dra7.dtsi | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm/boot/dts/dra7.dtsi b/arch/arm/boot/dts/dra7.dtsi
> index d78b684e7fca..058b8cbb8ef3 100644
> --- a/arch/arm/boot/dts/dra7.dtsi
> +++ b/arch/arm/boot/dts/dra7.dtsi
> @@ -148,6 +148,7 @@
>   		#address-cells = <1>;
>   		#size-cells = <1>;
>   		ranges = <0x0 0x0 0x0 0xc0000000>;
> +		dma-ranges = <0x80000000 0x0 0x80000000 0x80000000>;
>   		ti,hwmods = "l3_main_1", "l3_main_2";
>   		reg = <0x0 0x44000000 0x0 0x1000000>,
>   		      <0x0 0x45000000 0x0 0x1000>;
>