Re: [PATCH] mtd: nand: wait for tWHR after NAND_CMD_STATUS / NAND_CMD_READID

From	Boris Brezillon <boris.brezillon@free-electrons.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] mtd: nand: wait for tWHR after NAND_CMD_STATUS / NAND_CMD_READID
Date	2017-09-26 10:30 +0200
Message-ID	<utTpD-2dI-7@gated-at.bofh.it> (permalink)
References	<utP2F-7zs-7@gated-at.bofh.it> <utRQR-150-9@gated-at.bofh.it> <utTfY-29X-21@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Tue, 26 Sep 2017 17:17:49 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:

> 2017-09-26 15:43 GMT+09:00 Boris Brezillon <boris.brezillon@free-electrons.com>:
> > On Tue, 26 Sep 2017 12:39:24 +0900
> > Masahiro Yamada <yamada.masahiro@socionext.com> wrote:
> >  
> >> Read Status and Read ID require tWHR before reading the first data.
> >> Insert a very short wait to make sure to meet the spec.
> >>
> >> I have not seen any problem report for now, but nand_command() and
> >> nand_command_lP() are generic hooks, so it makes sense to implement
> >> fail-safe code here.
> >>
> >> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> >> ---  
> >  
> 
> 
> OK, will do.
> 
> 
> 
> BTW, I see unconditional wait for tWB a few lines below,
> but it gives no performance regression because we will wait
> much longer in nand_wait_ready().

Yep, but this one is here for quite some time. Normally there should be
no problem with your ndelay(200), but I don't want to take the risk
and have someone complain that his NAND controller driver is broken
because of this extra delay ;-).

> 
> 
>      /*
>       * Apply this short delay always to ensure that we do wait tWB in
>       * any case on any machine.
>       */
>      ndelay(100);
> 
>      nand_wait_ready(mtd);
> 
> 
> 
>

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH] mtd: nand: wait for tWHR after NAND_CMD_STATUS / NAND_CMD_READID Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-09-26 05:50 +0200
  Re: [PATCH] mtd: nand: wait for tWHR after NAND_CMD_STATUS /  NAND_CMD_READID Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-09-26 08:50 +0200
    Re: [PATCH] mtd: nand: wait for tWHR after NAND_CMD_STATUS / NAND_CMD_READID Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-09-26 10:20 +0200
      Re: [PATCH] mtd: nand: wait for tWHR after NAND_CMD_STATUS /  NAND_CMD_READID Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-09-26 10:30 +0200

csiph-web