linux-kernel - RE: memblock_end_of_DRAM() return end address + 1

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Date:	Thu, 31 May 2012 13:41:34 +0000
From:	Bhushan Bharat-R65777 <R65777@...escale.com>
To:	Bhushan Bharat-R65777 <R65777@...escale.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>, "hpa@...or.com" <hpa@...or.com>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	Wood Scott-B07421 <B07421@...escale.com>
CC:	"agraf@...e.de" <agraf@...e.de>
Subject: RE: memblock_end_of_DRAM()  return end address + 1

Adding some more gentlemen's.	


> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
> owner@...r.kernel.org] On Behalf Of Bhushan Bharat-R65777
> Sent: Thursday, May 31, 2012 4:34 PM
> To: linux-mm@...ck.org; linux-kernel@...r.kernel.org
> Cc: agraf@...e.de
> 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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