2012-05-31 11:04:30

by Bharat Bhushan

Subject: memblock_end_of_DRAM() return end address + 1

Hi All,

memblock_end_of_DRAM() defined in mm/memblock.c returns base_address + size;
So this is not returning the end_of_DRAM, it is basically returning the end_of_DRAM + 1. The name looks to suggest that this returns end address on DRAM.

IIUC, it looks like that some code assumes this returns the end address while some assumes this returns end address + 1.

Example:
1. arch/powerpc/platforms/85xx/mpc85xx_ds.c


<cut>

#ifdef CONFIG_SWIOTLB
if (memblock_end_of_DRAM() > max) {
ppc_swiotlb_enable = 1;
set_pci_dma_ops(&swiotlb_dma_ops);
ppc_md.pci_dma_dev_setup = pci_dma_dev_setup_swiotlb;
}
#endif

<cut>
<cut>


Where max = 0xffffffff; So we assumes that memblock_end_of_DRAM() actually returns end address.

------
2.

In arch/powerpc/kernel/dma.c


static int dma_direct_dma_supported(struct device *dev, u64 mask)
{
#ifdef CONFIG_PPC64
/* Could be improved so platforms can set the limit in case
* they have limited DMA windows
*/
return mask >= get_dma_offset(dev) + (memblock_end_of_DRAM() - 1);


<cut>

It looks to that here we assume base + addr + 1;

-----------


Thanks
-Bharat

2012-05-31 13:41:40

by Bharat Bhushan

Subject: RE: memblock_end_of_DRAM() return end address + 1

Adding some more gentlemen's.


> -----Original Message-----
> From: [email protected] [mailto:linux-kernel-
> [email protected]] On Behalf Of Bhushan Bharat-R65777
> Sent: Thursday, May 31, 2012 4:34 PM
> To: [email protected]; [email protected]
> Cc: [email protected]
> Subject: memblock_end_of_DRAM() return end address + 1
>
> Hi All,
>
> memblock_end_of_DRAM() defined in mm/memblock.c returns base_address + size; So
> this is not returning the end_of_DRAM, it is basically returning the end_of_DRAM
> + 1. The name looks to suggest that this returns end address on DRAM.
>
> IIUC, it looks like that some code assumes this returns the end address while
> some assumes this returns end address + 1.
>
> Example:
> 1. arch/powerpc/platforms/85xx/mpc85xx_ds.c
>
>
> <cut>
>
> #ifdef CONFIG_SWIOTLB
> if (memblock_end_of_DRAM() > max) {
> ppc_swiotlb_enable = 1;
> set_pci_dma_ops(&swiotlb_dma_ops);
> ppc_md.pci_dma_dev_setup = pci_dma_dev_setup_swiotlb;
> }
> #endif
>
> <cut>
> <cut>
>
>
> Where max = 0xffffffff; So we assumes that memblock_end_of_DRAM() actually
> returns end address.
>
> ------
> 2.
>
> In arch/powerpc/kernel/dma.c
>
>
> static int dma_direct_dma_supported(struct device *dev, u64 mask) { #ifdef
> CONFIG_PPC64
> /* Could be improved so platforms can set the limit in case
> * they have limited DMA windows
> */
> return mask >= get_dma_offset(dev) + (memblock_end_of_DRAM() - 1);
>
>
> <cut>
>
> It looks to that here we assume base + addr + 1;
>
> -----------
>
>
> Thanks
> -Bharat
>
>
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