linux-kernel - Re: [PATCH v5 13/15] MIPS: JZ4770: Workaround for corrupted DMA transfers

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Date:   Fri, 05 Jan 2018 19:03:52 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        Maarten ter Huurne <maarten@...ewalker.org>,
        devicetree@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        linux-mips@...ux-mips.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH v5 13/15] MIPS: JZ4770: Workaround for corrupted DMA
 transfers

Hi,
Hi,

>> [...]
>> 
>>  +/*
>>  + * 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?

I guess it would work as well, but I don't think this fix should be in 
devicetree.

-Paul