[U-Boot] [PATCH] net: fec: Avoid MX28 bus sync issue

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hi Troy,

On Fri, 12 Jul 2013 19:43:07 -0700, Troy Kisky
<troy.kisky@boundarydevices.com> wrote:

> On 7/11/2013 4:18 PM, Fabio Estevam wrote:
> > On Thu, Jul 11, 2013 at 8:03 PM, Marek Vasut <marex@denx.de> wrote:
> >> The MX28 multi-layer AHB bus can be too slow and trigger the
> >> FEC DMA too early, before all the data hit the DRAM. This patch
> >> ensures the data are written in the RAM before the DMA starts.
> >> Please see the comment in the patch for full details.
> >>
> >> This patch was produced with an amazing help from Albert Aribaud,
> >> who pointed out it can possibly be such a bus synchronisation
> >> issue.
> >>
> >> Signed-off-by: Marek Vasut <marex@denx.de>
> >> Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
> >> Cc: Fabio Estevam <fabio.estevam@freescale.com>
> >> Cc: Stefano Babic <sbabic@denx.de>
> > Excellent, managed to transfer 90MB via TFTP on mx28evk without a
> > single timeout.
> >
> > Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
> > _______________________________________________
> > U-Boot mailing list
> > U-Boot at lists.denx.de
> > http://lists.denx.de/mailman/listinfo/u-boot
> >
> Perhaps this because our memory barriers are lacking.
> 
> Linux has this code
> asm/io.h:#define writel(v,c)            ({ __iowmb(); 
> writel_relaxed(v,c); })
> 
> asm/io.h-#ifdef CONFIG_ARM_DMA_MEM_BUFFERABLE
> asm/io.h-#include <asm/barrier.h>
> asm/io.h-#define __iormb()              rmb()
> asm/io.h:#define __iowmb()              wmb()
> asm/io.h-#else
> asm/io.h-#define __iormb()              do { } while (0)
> asm/io.h:#define __iowmb()              do { } while (0)
> asm/io.h-#endif
> 
> asm/io.h-#ifdef CONFIG_ARM_DMA_MEM_BUFFERABLE
> asm/io.h-#include <asm/barrier.h>
> asm/io.h-#define __iormb()              rmb()
> asm/io.h:#define __iowmb()              wmb()
> asm/io.h-#else
> asm/io.h-#define __iormb()              do { } while (0)
> asm/io.h:#define __iowmb()              do { } while (0)
> asm/io.h-#endif
> 
> asm/barrier.h-#elif defined(CONFIG_ARM_DMA_MEM_BUFFERABLE) || 
> defined(CONFIG_SMP)
> asm/barrier.h-#define mb()              do { dsb(); outer_sync(); } 
> while (0)
> asm/barrier.h-#define rmb()             dsb()
> asm/barrier.h:#define wmb()             mb()
> asm/barrier.h-#else
> asm/barrier.h-#define mb()              barrier()
> asm/barrier.h-#define rmb()             barrier()
> asm/barrier.h:#define wmb()             barrier()
> asm/barrier.h-#endif
> 
> asm/barrier.h-#if __LINUX_ARM_ARCH__ >= 7
> asm/barrier.h-#define isb() __asm__ __volatile__ ("isb" : : : "memory")
> asm/barrier.h:#define dsb() __asm__ __volatile__ ("dsb" : : : "memory")
> asm/barrier.h-#define dmb() __asm__ __volatile__ ("dmb" : : : "memory")
> asm/barrier.h-#elif defined(CONFIG_CPU_XSC3) || __LINUX_ARM_ARCH__ == 6
> asm/barrier.h-#define isb() __asm__ __volatile__ ("mcr p15, 0, %0, c7, 
> c5, 4" \
> asm/barrier.h-                              : : "r" (0) : "memory")
> asm/barrier.h:#define dsb() __asm__ __volatile__ ("mcr p15, 0, %0, c7, 
> c10, 4" \
> asm/barrier.h-                              : : "r" (0) : "memory")
> asm/barrier.h-#define dmb() __asm__ __volatile__ ("mcr p15, 0, %0, c7, 
> c10, 5" \
> 
> _____________________________________
> Can you try just adding a dsb() instead of the dummy read?
> 
> If this also fixes your problem, it seems better to fix our writel macro

Not sure I understand who you are answering to exactly, as Fabio
indicates his problem is solved.

Besides, Marek and I had in fact investigated barriers, adding some as
I did in times past in mvgbe.c, and fiddling with the one already in
dcache_flush_range(). None of this had any effect.

However, if our barriers are lacking, then they may fail us somehow on
other occasions, so best is if we analyze the failings. Can you clarify
in what respect exactly they are lacking? For instance, are all our
barriers lacking, or only some, and which ones?

Amicalement,
-- 
Albert.