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Subject: Re: [PATCH v13 2/8] mtd: rawnand: rockchip: NFC drivers for RK3308,
 RK2928 and others
To:     Miquel Raynal <miquel.raynal@bootlin.com>
Cc:     Yifeng <yifeng.zhao@rock-chips.com>, richard@nod.at,
        vigneshr@ti.com, robh+dt@kernel.org, devicetree@vger.kernel.org,
        heiko@sntech.de, linux-kernel@vger.kernel.org,
        linux-rockchip@lists.infradead.org, linux-mtd@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org
References: <20201028095326.15562-1-yifeng.zhao@rock-chips.com>
 <20201028095326.15562-3-yifeng.zhao@rock-chips.com>
 <a8a7875b-f08b-62c6-a630-245687e0df3b@gmail.com>
 <e02e13a0-769d-6b73-c87e-5b7d75fd4254@rock-chips.com>
 <0b417fc2-3503-9bf6-914d-0f8b38df1914@gmail.com>
 <20201102140725.66e7dcb1@xps13>
 <5ad70fa0-05a9-e1e7-32cc-32933ff25ae9@gmail.com>
 <803e291f-67e0-f66c-6c9e-041db1b3847c@gmail.com>
 <20201102180039.757d3234@xps13>
From:   Johan Jonker <jbx6244@gmail.com>
Message-ID: <cd349a1f-773d-096a-f0ae-90c5eb847769@gmail.com>
Date:   Mon, 2 Nov 2020 18:11:52 +0100
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On 11/2/20 6:00 PM, Miquel Raynal wrote:
> Hi Johan,
> 
> Johan Jonker <jbx6244@gmail.com> wrote on Mon, 2 Nov 2020 17:31:18
> +0100:
> 
>> On 11/2/20 2:11 PM, Johan Jonker wrote:
>>> Hi,
>>>
>>> On 11/2/20 2:07 PM, Miquel Raynal wrote:
>>>> Hi Johan, Yifeng
>>>>
>>>> Johan Jonker <jbx6244@gmail.com> wrote on Mon, 2 Nov 2020 13:57:56
>>>> +0100:
>>>>
>>>>> Hi Yifeng,
>>>>>
>>>>> Don't poke with "ecc->bytes" ones it is set in rk_nfc_ecc_init(). It
>>>>> will not be noted by the MTD frame work or userspace. I think there's
>>>>> currently no way to let the user know that a different ECC must be used.
>>>>> Neither can the user set ECC on the fly.
>>>>>
>>>>> Example R/W flow:
>>>>>
>>>>>         nand_select_target()
>>>>> 	chip->ecc.write_page_raw()
>>>>> 	chip->ecc.write_page()
>>>>>
>>>>> [..]
>>>>>
>>>>> 	chip->ecc.read_page_raw()
>>>>> 	chip->ecc.read_page()
>>>>>         nand_deselect_target()
>>>>>
>>>>> A write/read with:
>>>>>
>>>>> rk_nfc_read_page_hwecc()
>>>>> rk_nfc_write_page_hwecc()
>>>>>
>>>>> or
>>>>>
>>>>> rk_nfc_read_page_raw()
>>>>> rk_nfc_write_page_raw()
>>>>>
>>>>> must end up with the same result. If we can't archive that, then we
>>>>> shouldn't offer RAW mode to the user for now. If Miquel agrees you
>>>>> should just get the driver ready now without these 2 functions and round
>>>>> things up.
>>>>
>>>> What about just not supporting the BootROM area if it was marked
>>>> "reserved" by the BRom in the DT?
>>>
>>> Should we just fill the buffers with '0xff' for boot blocks?
>>
>> (part 2) ;)
>> My fault....
>> Better use:
>>
>>     if ((chip->options & NAND_IS_BOOT_MEDIUM) &&
>>         (page < (pages_per_blk * rknand->boot_blks))) {
>>
>> 	return -EIO;
>>
>>     }
> 
> Yup, I was about to tell you that I would prefer returning a nice
> error, this is fine I guess.
> 
> Anyway, I think reading bad block markers is done in raw mode, so if
> raw accessors refuse to return valid values for boot blocks, you won't
> be able to access it neither with raw nor corrected hooks.
> 
> Perhaps refusing the access to the regular page access is ok, but maybe
> we should be able to at least read these pages in raw mode
> (and move the BBM to its right location). What do you think?

I think that the problem with asymmetric read and write access is that a
user reads data successful, but that it can't write it back after it's
block is erased. You shouldn't give the illusion that the boot ROM
blocks can be accessed in RAW mode. Something with perception...does
user space known that Rockchip's NFC is special...


> 
> Thanks,
> Miquèl
> 
>>
>>
>>>
>>>>
>>>> Raw accessors is really a nice and basic feature that I would like to
>>>> have in every new driver.
>>>>
>>>> Thanks,
>>>> Miquèl
>>>>
>>>
>>