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

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Date:   Thu, 30 Apr 2020 15:50:30 +0800
From:   "Ramuthevar, Vadivel MuruganX" 
        <vadivel.muruganx.ramuthevar@...ux.intel.com>
To:     Boris Brezillon <boris.brezillon@...labora.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

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 
ADDR_SELx , it compares only 5 bits.

> 
>>
>>>>>       
>>>>>> +#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?

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

Regards
Vadivel
>