Re: [PATCH 2/3] Revert "bus: mvebu-mbus: make sure SDRAM CS for DMA don't overlap the MBus bridge window"

[Gregory CLEMENT <gregory.clement@free-electrons.com>]

Hi Thomas,

On 28/05/2015 10:40, Thomas Petazzoni wrote:
> This reverts commit 1737cac69369 ("bus: mvebu-mbus: make sure SDRAM CS
> for DMA don't overlap the MBus bridge window"), because it breaks DMA
> on platforms having more than 2 GB of RAM.
> 
> This commit changed the information reported to DMA masters device
> drivers through the mv_mbus_dram_info() function so that the returned
> DRAM ranges do not overlap with I/O windows.
> 
> This was necessary as a preparation to support the new CESA Crypto
> Engine driver, which will use DMA for cryptographic operations. But
> since it does DMA with the SRAM which is mapped as an I/O window,
> having DRAM ranges overlapping with I/O windows was problematic.
> 
> To solve this, the above mentioned commit changed the mvebu-mbus to
> adjust the DRAM ranges so that they don't overlap with the I/O
> windows. However, by doing this, we re-adjust the DRAM ranges in a way
> that makes them have a size that is no longer a power of two. While
> this is perfectly fine for the Crypto Engine, which supports DRAM
> ranges with a granularity of 64 KB, it breaks basically all other DMA
> masters, which expect power of two sizes for the DRAM ranges.
> 
> Due to this, if the installed system memory is 4 GB, in two
> chip-selects of 2 GB, the second DRAM range will be reduced from 2 GB
> to a little bit less than 2 GB to not overlap with the I/O windows, in
> a way that results in a DRAM range that doesn't have a power of two
> size. This means that whenever you do a DMA transfer with an address
> located in the [ 2 GB ; 4 GB ] area, it will freeze the system. Any
> serious DMA activity like simply running:
> 
>   for i in $(seq 1 64) ; do dd if=/dev/urandom of=file$i bs=1M count=16 ; done
> 
> in an ext3 partition mounted over a SATA drive will freeze the system.
> 
> Since the new CESA crypto driver that uses DMA has not been merged
> yet, the easiest fix is to simply revert this commit. A follow-up
> commit will introduce a different solution for the CESA crypto driver.
> 
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Fixes: 1737cac69369 ("bus: mvebu-mbus: make sure SDRAM CS for DMA don't overlap the MBus bridge window")
> Cc: <stable@vger.kernel.org> # v4.0+

applied on mvebu/fixes

I hope that the 100 lines rules will be not a problem for this case

Thanks,

Gregory


> ---
>  drivers/bus/mvebu-mbus.c | 105 ++++++++---------------------------------------
>  1 file changed, 16 insertions(+), 89 deletions(-)
> 
> diff --git a/drivers/bus/mvebu-mbus.c b/drivers/bus/mvebu-mbus.c
> index 7fa4510..6f047dc 100644
> --- a/drivers/bus/mvebu-mbus.c
> +++ b/drivers/bus/mvebu-mbus.c
> @@ -58,7 +58,6 @@
>  #include <linux/debugfs.h>
>  #include <linux/log2.h>
>  #include <linux/syscore_ops.h>
> -#include <linux/memblock.h>
>  
>  /*
>   * DDR target is the same on all platforms.
> @@ -103,9 +102,7 @@
>  
>  /* Relative to mbusbridge_base */
>  #define MBUS_BRIDGE_CTRL_OFF	0x0
> -#define  MBUS_BRIDGE_SIZE_MASK  0xffff0000
>  #define MBUS_BRIDGE_BASE_OFF	0x4
> -#define  MBUS_BRIDGE_BASE_MASK  0xffff0000
>  
>  /* Maximum number of windows, for all known platforms */
>  #define MBUS_WINS_MAX           20
> @@ -579,106 +576,36 @@ static unsigned int armada_xp_mbus_win_remap_offset(int win)
>  		return MVEBU_MBUS_NO_REMAP;
>  }
>  
> -/*
> - * Use the memblock information to find the MBus bridge hole in the
> - * physical address space.
> - */
> -static void __init
> -mvebu_mbus_find_bridge_hole(uint64_t *start, uint64_t *end)
> -{
> -	struct memblock_region *r;
> -	uint64_t s = 0;
> -
> -	for_each_memblock(memory, r) {
> -		/*
> -		 * This part of the memory is above 4 GB, so we don't
> -		 * care for the MBus bridge hole.
> -		 */
> -		if (r->base >= 0x100000000)
> -			continue;
> -
> -		/*
> -		 * The MBus bridge hole is at the end of the RAM under
> -		 * the 4 GB limit.
> -		 */
> -		if (r->base + r->size > s)
> -			s = r->base + r->size;
> -	}
> -
> -	*start = s;
> -	*end = 0x100000000;
> -}
> -
>  static void __init
>  mvebu_mbus_default_setup_cpu_target(struct mvebu_mbus_state *mbus)
>  {
>  	int i;
>  	int cs;
> -	uint64_t mbus_bridge_base, mbus_bridge_end;
>  
>  	mvebu_mbus_dram_info.mbus_dram_target_id = TARGET_DDR;
>  
> -	mvebu_mbus_find_bridge_hole(&mbus_bridge_base, &mbus_bridge_end);
> -
>  	for (i = 0, cs = 0; i < 4; i++) {
> -		u64 base = readl(mbus->sdramwins_base + DDR_BASE_CS_OFF(i));
> -		u64 size = readl(mbus->sdramwins_base + DDR_SIZE_CS_OFF(i));
> -		u64 end;
> -		struct mbus_dram_window *w;
> -
> -		/* Ignore entries that are not enabled */
> -		if (!(size & DDR_SIZE_ENABLED))
> -			continue;
> -
> -		/*
> -		 * Ignore entries whose base address is above 2^32,
> -		 * since devices cannot DMA to such high addresses
> -		 */
> -		if (base & DDR_BASE_CS_HIGH_MASK)
> -			continue;
> -
> -		base = base & DDR_BASE_CS_LOW_MASK;
> -		size = (size | ~DDR_SIZE_MASK) + 1;
> -		end = base + size;
> -
> -		/*
> -		 * Adjust base/size of the current CS to make sure it
> -		 * doesn't overlap with the MBus bridge hole. This is
> -		 * particularly important for devices that do DMA from
> -		 * DRAM to a SRAM mapped in a MBus window, such as the
> -		 * CESA cryptographic engine.
> -		 */
> +		u32 base = readl(mbus->sdramwins_base + DDR_BASE_CS_OFF(i));
> +		u32 size = readl(mbus->sdramwins_base + DDR_SIZE_CS_OFF(i));
>  
>  		/*
> -		 * The CS is fully enclosed inside the MBus bridge
> -		 * area, so ignore it.
> +		 * We only take care of entries for which the chip
> +		 * select is enabled, and that don't have high base
> +		 * address bits set (devices can only access the first
> +		 * 32 bits of the memory).
>  		 */
> -		if (base >= mbus_bridge_base && end <= mbus_bridge_end)
> -			continue;
> +		if ((size & DDR_SIZE_ENABLED) &&
> +		    !(base & DDR_BASE_CS_HIGH_MASK)) {
> +			struct mbus_dram_window *w;
>  
> -		/*
> -		 * Beginning of CS overlaps with end of MBus, raise CS
> -		 * base address, and shrink its size.
> -		 */
> -		if (base >= mbus_bridge_base && end > mbus_bridge_end) {
> -			size -= mbus_bridge_end - base;
> -			base = mbus_bridge_end;
> +			w = &mvebu_mbus_dram_info.cs[cs++];
> +			w->cs_index = i;
> +			w->mbus_attr = 0xf & ~(1 << i);
> +			if (mbus->hw_io_coherency)
> +				w->mbus_attr |= ATTR_HW_COHERENCY;
> +			w->base = base & DDR_BASE_CS_LOW_MASK;
> +			w->size = (size | ~DDR_SIZE_MASK) + 1;
>  		}
> -
> -		/*
> -		 * End of CS overlaps with beginning of MBus, shrink
> -		 * CS size.
> -		 */
> -		if (base < mbus_bridge_base && end > mbus_bridge_base)
> -			size -= end - mbus_bridge_base;
> -
> -		w = &mvebu_mbus_dram_info.cs[cs++];
> -		w->cs_index = i;
> -		w->mbus_attr = 0xf & ~(1 << i);
> -		if (mbus->hw_io_coherency)
> -			w->mbus_attr |= ATTR_HW_COHERENCY;
> -		w->base = base;
> -		w->size = size;
>  	}
>  	mvebu_mbus_dram_info.num_cs = cs;
>  }
> 


-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com