netdev - Re: [PATCH] net: macb: Align the dma and coherent dma masks

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Date:   Wed, 9 Feb 2022 11:15:56 +0000
From:   <conor.dooley@...rochip.com>
To:     <harini.katakam@...inx.com>, <andrei.pistirica@...rochip.com>,
        <claudiu.beznea@...rochip.com>, <davem@...emloft.net>,
        <kuba@...nel.org>, <nicolas.ferre@...rochip.com>
CC:     <harinikatakamlinux@...il.com>, <Conor.Dooley@...rochip.com>,
        <linux-kernel@...r.kernel.org>, <michal.simek@...inx.com>,
        <mstamand@...na.com>, <netdev@...r.kernel.org>,
        Conor Dooley <conor.dooley@...rochip.com>
Subject: Re: [PATCH] net: macb: Align the dma and coherent dma masks

> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> From: Marc St-Amand <mstamand@...na.com>
> 
> Single page and coherent memory blocks can use different DMA masks
> when the macb accesses physical memory directly. The kernel is clever
> enough to allocate pages that fit into the requested address width.
> 
> When using the ARM SMMU, the DMA mask must be the same for single
> pages and big coherent memory blocks. Otherwise the translation
> tables turn into one big mess.
> 
>   [   74.959909] macb ff0e0000.ethernet eth0: DMA bus error: HRESP not OK
>   [   74.959989] arm-smmu fd800000.smmu: Unhandled context fault: fsr=0x402, iova=0x3165687460, fsynr=0x20001, cbfrsynra=0x877, cb=1
>   [   75.173939] macb ff0e0000.ethernet eth0: DMA bus error: HRESP not OK
>   [   75.173955] arm-smmu fd800000.smmu: Unhandled context fault: fsr=0x402, iova=0x3165687460, fsynr=0x20001, cbfrsynra=0x877, cb=1
> 
> Since using the same DMA mask does not hurt direct 1:1 physical
> memory mappings, this commit always aligns DMA and coherent masks.
> 
> Signed-off-by: Marc St-Amand <mstamand@...na.com>
> Signed-off-by: Harini Katakam <harini.katakam@...inx.com>

Tested-by: Conor Dooley <conor.dooley@...rochip.com>

Fixes a DMA allocation failure for me on a non arm board, seen if
I only assigned DDR to 64 bit addresses. Without the change I was
getting the following page allocation error:

Starting network:
[    2.911830] ip: page allocation failure: order:2, mode:0xcc4(GFP_KERNEL|GFP_DMA32),nodemask=(null)
[    2.921256] CPU: 3 PID: 171 Comm: ip Not tainted 5.17.0-rc1-00640-g6cc001edd9ad #1
[    2.928915] Hardware name: Microchip PolarFire-SoC Icicle Kit (DT)
[    2.935147] Call Trace:
[    2.937626] [<ffffffff800047e0>] dump_backtrace+0x1c/0x24
[    2.943087] [<ffffffff807fcfce>] dump_stack_lvl+0x40/0x58
[    2.948547] [<ffffffff807fcffa>] dump_stack+0x14/0x1c
[    2.953649] [<ffffffff80104bfc>] warn_alloc+0xd6/0x14c
[    2.958849] [<ffffffff801053e0>] __alloc_pages_slowpath.constprop.0+0x76e/0x882
[    2.966242] [<ffffffff80105618>] __alloc_pages+0x124/0x174
[    2.971783] [<ffffffff80061440>] __dma_direct_alloc_pages+0x12c/0x28c
[    2.978286] [<ffffffff800616f2>] dma_direct_alloc+0x40/0x13e
[    2.983996] [<ffffffff80060bf2>] dma_alloc_attrs+0x78/0x86
[    2.989541] [<ffffffff805cdfb6>] macb_open+0x84/0x42c
[    2.994645] [<ffffffff806e2468>] __dev_open+0xb0/0x142
[    2.999845] [<ffffffff806e2884>] __dev_change_flags+0x180/0x1ec
[    3.005827] [<ffffffff806e290e>] dev_change_flags+0x1e/0x54
[    3.011461] [<ffffffff8076960e>] devinet_ioctl+0x1fc/0x612
[    3.017015] [<ffffffff8076b27e>] inet_ioctl+0x96/0xfa
[    3.022109] [<ffffffff806bf5e2>] sock_ioctl+0x256/0x29e
[    3.027396] [<ffffffff8012bc7c>] sys_ioctl+0x340/0x7f8
[    3.032595] [<ffffffff80003014>] ret_from_syscall+0x0/0x2
<snip>
[    3.176712] macb 20110000.ethernet eth0: Unable to allocate DMA memory (error -12)
ip: SIOCSIFFLAGS: Cannot allocate memory
FAIL