Re: [PATCH v2 15/17] MIPS: JZ4770: Workaround for corrupted DMA transfers

[Paul Cercueil]

Hi,

Le 2017-06-22 09:21, Marcin Nowakowski a ÃcritÂ:
> Hi Paul, Maarten,
>
> On 20.06.2017 17:18, Paul Cercueil wrote:
> > From: Maarten ter Huurne <maarten@xxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxx>
> > ---
> >   arch/mips/jz4740/setup.c | 24 ++++++++++++++++++++++++
> >   arch/mips/kernel/setup.c |  8 ++++++++
> >   2 files changed, 32 insertions(+)
> >
> >   v2: 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;
> > +	}
> > +}
> > +
> >   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 89785600fde4..cccfd7ba89fe 100644
> > --- a/arch/mips/kernel/setup.c
> > +++ b/arch/mips/kernel/setup.c
> > @@ -838,6 +838,14 @@ 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
> > +
>
> This part doesn't look good in the platform-agnostic code ... is there
> a reason why you wouldn't do that from within plat_mem_setup()?

I agree, but, doing it in plat_mem_setup() is too early, as the 'boot 
mem map' hasn't been initialized yet then...

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