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 23:18:31 +0800
From:   "Ramuthevar, Vadivel MuruganX" 
        <vadivel.muruganx.ramuthevar@...ux.intel.com>
To:     Boris Brezillon <boris.brezillon@...labora.com>,
        qi-ming.wu@...el.com
Cc:     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

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).

>>>    
>>>> +#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

>