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From: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Date: Tue, 2 Jan 2018 22:15:14 +0530
Message-ID: <CANc+2y4mJMMiN4SPiPtcXMrQ0AM_2XGnVRk1Dvyv9VYpNN3x-g@mail.gmail.com>
Subject: Re: [PATCH v5 13/15] MIPS: JZ4770: Workaround for corrupted DMA transfers
To: Paul Cercueil <paul@crapouillou.net>
Cc: Ralf Baechle <ralf@linux-mips.org>,
        Maarten ter Huurne <maarten@treewalker.org>,
        devicetree@vger.kernel.org,
        open list <linux-kernel@vger.kernel.org>,
        linux-mips@linux-mips.org, linux-clk@vger.kernel.org
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Sender: linux-kernel-owner@vger.kernel.org

Hi Paul,

On 2 January 2018 at 20:38, Paul Cercueil <paul@crapouillou.net> wrote:
> From: Maarten ter Huurne <maarten@treewalker.org>
>
> We have seen MMC DMA transfers read corrupted data from SDRAM when
> a burst interval ends at physical address 0x10000000. To avoid this
> problem, we remove the final page of low memory from the memory map.
>
> Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
> ---
>  arch/mips/jz4740/setup.c | 24 ++++++++++++++++++++++++
>  arch/mips/kernel/setup.c |  8 ++++++++
>  2 files changed, 32 insertions(+)
>
>  v2: No change
>  v3: No change
>  v4: No change
>  v5: No change
>
> diff --git a/arch/mips/jz4740/setup.c b/arch/mips/jz4740/setup.c
> index afd84ee966e8..6948b133a15d 100644
> --- a/arch/mips/jz4740/setup.c
> +++ b/arch/mips/jz4740/setup.c
> @@ -23,6 +23,7 @@
>
>  #include <asm/bootinfo.h>
>  #include <asm/mips_machine.h>
> +#include <asm/page.h>
>  #include <asm/prom.h>
>
>  #include <asm/mach-jz4740/base.h>
> @@ -102,6 +103,29 @@ void __init arch_init_irq(void)
>         irqchip_init();
>  }
>
> +/*
> + * We have seen MMC DMA transfers read corrupted data from SDRAM when a burst
> + * interval ends at physical address 0x10000000. To avoid this problem, we
> + * remove the final page of low memory from the memory map.
> + */
> +void __init jz4770_reserve_unsafe_for_dma(void)
> +{
> +       int i;
> +
> +       for (i = 0; i < boot_mem_map.nr_map; i++) {
> +               struct boot_mem_map_entry *entry = boot_mem_map.map + i;
> +
> +               if (entry->type != BOOT_MEM_RAM)
> +                       continue;
> +
> +               if (entry->addr + entry->size != 0x10000000)
> +                       continue;
> +
> +               entry->size -= PAGE_SIZE;
> +               break;
> +       }
> +}
> +

Just a wild idea (probably bad too). Changing the memory node in the
device tree to skip this physical address would work I think. What is
your opinion about that?

>  static int __init jz4740_machine_setup(void)
>  {
>         mips_machine_setup();
> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> index 85bc601e9a0d..5a2c20145aee 100644
> --- a/arch/mips/kernel/setup.c
> +++ b/arch/mips/kernel/setup.c
> @@ -879,6 +879,14 @@ static void __init arch_mem_init(char **cmdline_p)
>
>         parse_early_param();
>
> +#ifdef CONFIG_MACH_JZ4770
> +       if (current_cpu_type() == CPU_JZRISC &&
> +                               mips_machtype == MACH_INGENIC_JZ4770) {
> +               extern void __init jz4770_reserve_unsafe_for_dma(void);
> +               jz4770_reserve_unsafe_for_dma();
> +       }
> +#endif
> +
>         if (usermem) {
>                 pr_info("User-defined physical RAM map:\n");
>                 print_memory_map();
> --
> 2.11.0
>
>

Thanks,
PrasannaKumar