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

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Date:   Wed, 29 Apr 2020 17:31:07 +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 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).

> 
> >>>      
> >>>> +#define EBU_ADDR_SEL_REGEN	0x1  
> >>>
> >>>      
> >>>> +
> >>>> +	writel(lower_32_bits(ebu_host->cs[ebu_host->cs_num].nand_pa) |
> >>>> +	       EBU_ADDR_SEL_REGEN | EBU_ADDR_MASK,
> >>>> +	       ebu_host->ebu + EBU_ADDR_SEL(reg));

You set EBU_ADDR_SEL(reg) once here...

> >>>> +
> >>>> +	writel(EBU_MEM_BASE_CS_0 | EBU_ADDR_MASK | EBU_ADDR_SEL_REGEN,
> >>>> +	       ebu_host->ebu + EBU_ADDR_SEL(0));
> >>>> +	writel(EBU_MEM_BASE_CS_1 | EBU_ADDR_MASK | EBU_ADDR_SEL_REGEN,
> >>>> +	       ebu_host->ebu + EBU_ADDR_SEL(reg));  

... and a second time here. That sounds like overwriting the
EBU_ADDR_SEL(reg) register to me.

> >>>
> >>> That's super weird. You seem to set EBU_ADDR_SEL(reg) twice. Are you
> >>> sure that's needed, and are we setting EBU_ADDR_SEL(0) here?  
> >>
> >> You are right, its weird only, but we need it, since different chip
> >> select has different memory region access address.  
> > 
> > Well, that doesn't make any sense, the second write to
> > EBU_ADDR_SEL(reg) overrides the first one, meaning that nand_pa is
> > actually never written to ADDR_SEL(reg).  
> 
> it will not overwrite the first one, since two different registers
> EBU_ADDR_SEL_0 EBU_ADDR_SEL  20H
> EBU_ADDR_SEL_1 EBU_ADDR_SEL  24H

See my above.

> 
> it is an internal address selection w.r.t chip select for nand physical 
> address update.
> 
> 
> >   
> >>
> >> 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?