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Date:   Thu, 30 Apr 2020 14:36:00 +0200
From:   Boris Brezillon <boris.brezillon@collabora.com>
To:     "Ramuthevar, Vadivel MuruganX" 
        <vadivel.muruganx.ramuthevar@linux.intel.com>
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Subject: Re: [PATCH v4 2/2] mtd: rawnand: Add NAND controller support on
 Intel LGM SoC
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On Thu, 30 Apr 2020 17:07:03 +0800
"Ramuthevar, Vadivel MuruganX"
<vadivel.muruganx.ramuthevar@linux.intel.com> wrote:

> >>> The question is, is it the same value we have in nand_pa or it is
> >>> different?
> >>>      
> >> Different address which is 0xE1400000 NAND_BASE_PHY address.  
> > 
> > Then why didn't you tell me they didn't match when I suggested to pass  
> 
> sorry, because you keep asking nand_pa after that only I realized that.
> 
> > nand_pa? So now the question is, what does this address represent?  
> 
>                 EBU-MODULE
>   _________     _______________________
> |         |   |            |NAND CTRL  |
> | FPI BUS |==>| CS0(0x174) | 0xE100    ( 0xE14/0xE1C) NAND_PHY_BASE
> |_________|   |_CS1(0x17C)_|__________ |
> 
> EBU_CONRTROLLER_BASE : 0xE0F0_0000
> HSNAND_BASE: 0xE100_0000
> NAND_CS0: 0xE140_0000
> NAND_CS1: 0xE1C0_0000
> 
> MEM_REGION_BASE_CS0: 0x17400 (internal to ebu controller )
> MEM_REGION_BASE_CS1: 0x17C00
> 

Hm, I wonder if we shouldn't use a 'ranges' property to describe this
address translation. Something like

	ebu@xxx {
		ranges = <0x17400000 0xe1400000 0x1000>,
			 <0x17c00000 0xe1c00000 0x1000>;
		reg = <0x17400000>, <0x17c00000>;
		reg-names = "cs-0", "cs-1";
	}

The translated address (0xE1X00000) will be available in res->start,
and the non-translated one (0x17X00000) can be retrieved with
of_get_address(). All you'd have to do then would be calculate the
mask:

	mask = (translated_address & original_address) >> 22;
	num_comp_bits = fls(mask);
	WARN_ON(mask != GENMASK(num_comp_bits - 1, 0));

Which allows you to properly set the ADDR_SEL() register without
relying on some hardcoded values:

	writel(original_address | EBU_ADDR_SEL_REGEN |
	       EBU_ADDR_COMP_BITS(num_comp_bits),
	       ebu_host->ebu + EBU_ADDR_SEL(csid));

That's quite important if we want to merge the xway NAND driver with
this one.