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    SubjectRe: [PATCH v6 13/15] MIPS: JZ4770: Workaround for corrupted DMA transfers
    On Fri, Jan 05, 2018 at 07:25:11PM +0100, Paul Cercueil 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
    > v6: No change
    >
    > diff --git a/arch/mips/jz4740/setup.c b/arch/mips/jz4740/setup.c
    > index cd89536fbba1..18c57c4bf47e 100644
    > --- a/arch/mips/jz4740/setup.c
    > +++ b/arch/mips/jz4740/setup.c
    > @@ -22,6 +22,7 @@
    > #include <linux/of_fdt.h>
    >
    > #include <asm/bootinfo.h>
    > +#include <asm/page.h>
    > #include <asm/prom.h>
    >
    > #include <asm/mach-jz4740/base.h>
    > @@ -103,3 +104,26 @@ 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;
    > + }
    > +}
    > 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

    Hmm, a little bit ugly. I'm guessing the plat_mem_setup() callback is
    too early since mem= parameters won't have been taken into account yet
    from parse_early_param().

    Is /memreserve/ in FDT of any value here or is it all too late due to
    old DTs?

    Cheers
    James

    > +
    > if (usermem) {
    > pr_info("User-defined physical RAM map:\n");
    > print_memory_map();
    > --
    > 2.11.0
    >
    >
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