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

Ramuthevar, Vadivel MuruganX
2020-04-30T07:50:38Z

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@linux.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@linux.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@linux.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
>