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SubjectRe: [PATCH v2 0/2] mtd: nand: wait for tWHR, and fix the setup_data_interface of Denali
On Fri, 29 Sep 2017 23:06:42 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:

> 2017-09-29 21:26 GMT+09:00 Boris Brezillon <boris.brezillon@free-electrons.com>:
> > On Fri, 29 Sep 2017 19:38:38 +0900
> > Masahiro Yamada <yamada.masahiro@socionext.com> wrote:
> >
> >> 1/2 : add NAND_WAIT_TWHR and nand_whr_delay().
> >> You can set this new flag if you want nand_command(_lp)
> >> to insert tWHR delay where needed.
> >>
> >> 2/2 : Fix Denali setup_data_interface.
> >> Boris' suggestion in v1 was a good reminder that
> >> made me realize tCCS was missing in the driver. Fix it now.
> >>
> >>
> >> Changes in v2:
> >> - Add nand_whr_delay() helper
> >> Wait for tWHR only for drivers that explicitly set NAND_WAIT_TWHR flag
> >> - newly added
> >>
> >> Masahiro Yamada (2):
> >> mtd: nand: wait for tWHR after NAND_CMD_STATUS / NAND_CMD_READID
> >
> > Hm, I thought you were introducing this to then use it in the denali
> > driver. Sorry, but I don't want to apply something that nobody needs.
> > If someone ever complains about a missing delay I'll point him to your
> > patch, but until then I'll keep the core unchanged.
>
>
> At first, I thought this was necessary for me,
> but I realized it was my misunderstanding.
>
>
> Please let me explain one more.
>
> See commit 3158fa0e739615769cc047d2428f30f4c3b6640e.
>
> Prior to that commit, READID waited for #R/B transition,
> it was wrong, so I fixed it.
>
> However, it dropped the delay completely.
> If somebody was implicitly relying on the delay of chip->dev_ready,
> the first byte might be read out before the valid data
> is available.
>
> This was motivation of v1, where inserted ndelay(200)
> unconditionally.

Okay. Anyway, this extra delay is activated with an opt-in flag (I
know, I'm the one who asked that), and noone set this flag in
chip->options, so, if there's a bug, it's still here even after
applying "mtd: nand: wait for tWHR after NAND_CMD_STATUS /
NAND_CMD_READID".

Honestly, I think all advanced controllers have the tWHR/tRHW timings
enforced in the HW logic (configurable through a reg). This leaves
basic controllers like the nand-gpio one, and even for these ones, the
delay between the chip->cmd_ctrl(ADDR) and chip->read_buf() calls is
probably long enough to hide the problem.

Note that I'm absolutely not against this patch, it's just that I'd
like to have a real user before merging this logic.

>
>
>
>
>
> >> mtd: nand: denali: fix setup_data_interface to meet tCCS delay
> >
> > This one is valid. I'll queue it to nand/next soon.
>
> If you drop 1/2, please let me do v3.
>
> V2 mentions NAND_WAIT_TWHR, this is strange.
>

Sure.

>
>

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