linux-kernel - Re: [PATCH v4 2/2] mtd: rawnand: Add NAND controller support on Intel LGM SoC

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Message-ID: <20200430102114.29b6552f@collabora.com>
Date:   Thu, 30 Apr 2020 10:21:14 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     "Ramuthevar, Vadivel MuruganX" 
        <vadivel.muruganx.ramuthevar@...ux.intel.com>
Cc:     qi-ming.wu@...el.com, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        cheol.yong.kim@...el.com, hauke.mehrtens@...el.com,
        anders.roxell@...aro.org, vigneshr@...com, arnd@...db.de,
        richard@....at, brendanhiggins@...gle.com,
        linux-mips@...r.kernel.org, robh+dt@...nel.org,
        miquel.raynal@...tlin.com, tglx@...utronix.de,
        masonccyang@...c.com.tw, andriy.shevchenko@...el.com
Subject: Re: [PATCH v4 2/2] mtd: rawnand: Add NAND controller support on
 Intel LGM SoC

On Thu, 30 Apr 2020 15:50:30 +0800
"Ramuthevar, Vadivel MuruganX"
<vadivel.muruganx.ramuthevar@...ux.intel.com> wrote:

> Hi Boris,
> 
>    Thank you very much for keep reviewing the patches and more queries...
> 
> On 29/4/2020 11:31 pm, Boris Brezillon wrote:
> > On Wed, 29 Apr 2020 23:18:31 +0800
> > "Ramuthevar, Vadivel MuruganX"
> > <vadivel.muruganx.ramuthevar@...ux.intel.com> wrote:
> >   
> >> Hi Boris,
> >>
> >> On 29/4/2020 10:48 pm, Boris Brezillon wrote:  
> >>> On Wed, 29 Apr 2020 22:33:37 +0800
> >>> "Ramuthevar, Vadivel MuruganX"
> >>> <vadivel.muruganx.ramuthevar@...ux.intel.com> wrote:
> >>>      
> >>>> Hi Boris,
> >>>>
> >>>> On 29/4/2020 10:22 pm, Boris Brezillon wrote:  
> >>>>> On Wed, 29 Apr 2020 18:42:05 +0800
> >>>>> "Ramuthevar, Vadivel MuruganX"
> >>>>> <vadivel.muruganx.ramuthevar@...ux.intel.com> wrote:
> >>>>>         
> >>>>>> +
> >>>>>> +#define EBU_ADDR_SEL(n)		(0x20 + (n) * 4)
> >>>>>> +#define EBU_ADDR_MASK		(5 << 4)  
> >>>>>
> >>>>> It's still unclear what ADDR_MASK is for. Can you add a comment
> >>>>> explaining what it does?  
> >>>>
> >>>> Thank you Boris, keep review and giving inputs, will update.  
> >>>
> >>> Can you please explain it here before sending a new version?  
> >>
> >> Memory Region Address Mask:
> >> Specifies the number of right-most bits in the base address that should
> >> be included in the address comparison. bits positions(7:4).  
> > 
> > Okay, then the macro should be
> > 
> > #define EBU_ADDR_MASK(x)	((x) << 4)
> > 
> > And now I'd like you to explain why 5 is the right value for that field
> > (I guess that has to do with the position of the CS/ALE/CLE pins).  
> 
> 5 : bit 26, 25, 24, 23, 22 to be included for comparison in the 

That's 6 bits to me, not 5.

> ADDR_SELx , it compares only 5 bits.

Definitely not what I would qualify as right-most bits. So, you say the
comparison always starts at bit 22, and ends at 22+<num-addr-bits>?

> >>>> Yes , we are setting both CS0 and CS1 memory access region, if you have
> >>>> any concern to optimize, please suggest me, Thanks!  
> >>>
> >>> If you want to setup both CS, and the address written in EBU_ADDR_SEL(x)
> >>> is really related to the nand_pa address, then retrieve resources for
> >>> all CS ranges.  
> >> If it's not related, please explain what those  
> >>> EBU_MEM_BASE_CS_X values encode.  
> >>
> >> Memory Region Base Address
> >> FPI Bus addresses are compared to this base address in conjunction with
> >> the mask control(EBU_ADDR_MASK). Driver need to program this field!  
> > 
> > That's not explaining what the base address should be. Is 'nand_pa' the
> > value we should have there?  
> 
> The one prorgrammed in the addr_sel register is used by the HW 
> controller, it remaps to  0x174XX-> CS0 and 0x17CXX->CS1.
> The hardware itself, decodes only for 1740xx/17c0xx, other random values 
> cannot be programmed

The question is, is it the same value we have in nand_pa or it is
different?