linux-kernel - Re: [PATCH v5 2/2] mtd: rawnand: Add NAND controller support on Intel LGM SoC

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Date:   Fri, 8 May 2020 10:31:19 +0800
From:   "Ramuthevar, Vadivel MuruganX" 
        <vadivel.muruganx.ramuthevar@...ux.intel.com>
To:     Boris Brezillon <boris.brezillon@...labora.com>
Cc:     linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
        devicetree@...r.kernel.org, miquel.raynal@...tlin.com,
        richard@....at, vigneshr@...com, arnd@...db.de,
        brendanhiggins@...gle.com, tglx@...utronix.de,
        anders.roxell@...aro.org, masonccyang@...c.com.tw,
        robh+dt@...nel.org, linux-mips@...r.kernel.org,
        hauke.mehrtens@...el.com, andriy.shevchenko@...el.com,
        qi-ming.wu@...el.com, cheol.yong.kim@...el.com
Subject: Re: [PATCH v5 2/2] mtd: rawnand: Add NAND controller support on Intel
 LGM SoC

Hi Boris,

   Thank you very much for the review comments and your time...
On 7/5/2020 2:48 pm, Boris Brezillon wrote:
 > On Thu, 7 May 2020 14:38:52 +0800
 > "Ramuthevar, Vadivel MuruganX"
 > <vadivel.muruganx.ramuthevar@...ux.intel.com> wrote:
 >
 >> Hi Boris,
 >>
 >>    Thank you very much for the review comments and your time...
 >>
 >> On 7/5/2020 2:27 pm, Boris Brezillon wrote:
 >>> On Thu, 7 May 2020 14:13:42 +0800
 >>> "Ramuthevar, Vadivel MuruganX"
 >>> <vadivel.muruganx.ramuthevar@...ux.intel.com> wrote:
 >>>
 >>>> Hi Boris,
 >>>>
 >>>>      Thank you very much for the review comments and your time...
 >>>>
 >>>> On 7/5/2020 1:28 pm, Boris Brezillon wrote:
 >>>>> On Thu,  7 May 2020 08:15:37 +0800
 >>>>> "Ramuthevar,Vadivel MuruganX"
 >>>>> <vadivel.muruganx.ramuthevar@...ux.intel.com> wrote:
 >>>>>
 >>>>>> +	reg = readl(ebu_host->ebu + EBU_ADDR_SEL(ebu_host->cs_num));
 >>>>>> +	writel(reg | EBU_ADDR_MASK(5) | EBU_ADDR_SEL_REGEN,
 >>>>>> +	       ebu_host->ebu + EBU_ADDR_SEL(ebu_host->cs_num));
 >>>>> Seriously, did you really think I would not notice what you're doing
 >>>>> here?
 >>>> Yes , I know that you have very good understanding about this.
 >>>>    You're reading the previous value which either contains a default
 >>>>> mapping or has the mapping set by the bootloader, and write it 
back to
 >>>>> the register along with a new mask and the REGEN bit set (which
 >>>>> BTW is wrong since you don't mask out other fields before updating
 >>>>> them).
 >>>> There is no other field get overwritten
 >>>>    This confirms that this Core -> FPI address translation exists
 >>>>> and has to be set properly, so please stop lying about that.
 >>>> Sorry, there is no SW translation, as I have mentioned that it's
 >>>> optional only, for safer side , reading and writing the default 
values.
 >>> Then write EBU_ADDR_SEL_REGEN and we'll if see that works. I suspect it
 >>> won't.
 >> You mean, without reading just writing EBU_ADDR_SEL_REGEN bit alone in
 >> EBU_ADDR_SELx , as you said it won't work because it overwrites 0x174
 >> with 0x0 values so BASE is lost.
 > Which confirms that this mapping has to be defined.
Sure, Noted.
 >> either we can leave it or read & write with ORed | EBU_ADDR_SEL_REGEN
 > None of this is acceptable IMO. You have to build the value based on the
 > address translation described in the DT. Why are you so reluctant to
 > this approach?
Agreed!, will derive the values(0x174/0x17C) to be written into these 
registers based on the chip select (CS0/CS1)
Address_sel0_register: 0xE0F0_0020
Address_sel1_register: 0xE0F0_0024
Bits : 31...12|11...8| 7..4 |3..2|  1   |  0
flags:  BASE  |------| MASK | -- | MRME | REGEN

BASE : 0x17400 /0x17C00 to be written into 31:12 based on the chip selection
MASK: 5: bits 26:22 to included address comparison
MRME: Memory Region Memory Enable
REGEN: Memory Region Access Enable

As you have suggested to get the above base values from DT and update in 
driver, will do that.

Thanks!
Regards
Vadivel
 >> Please correct me if anything is wrong, Thanks!
 >>>
 >>>> The memory region to enabled that's my concern so written the same
 >>>> register values.
 >>> I don't buy that, sorry.
 >>>
 >>>> This will not be impact other fields, so please see below for 
reference
 >>>>
 >>>> The EBU Address Select Registers EBU_ADDR_SEL_0 to EBU_ADDSEL3 
establish
 >>>> and control memory regions for external accesses.
 >>>>
 >>>> Reset Value: 17400001H
 >>> See, as suspected the reset value is exactly what you expect.
 >> Yes , that's the reason said being optional.
 > Then it's not optional. It just works because you use the default
 > va