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

[Ramuthevar, Vadivel MuruganX]

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@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> 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).

> > >    
> > > > +#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));
> > > > +
> > > > +	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));
> > >
> > > 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

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!

Regards
Vadivel

>