Re: [PATCH] mtd: spi-nor: scale up timeout for full-chip erase

[Brian Norris <computersforpeace@gmail.com>]

On Fri, Sep 18, 2015 at 02:59:17PM -0700, Brian Norris wrote:
> From: Furquan Shaikh <furquan@google.com>
> 
> This patch fixes timeout issues seen on large NOR flash (e.g., 16MB
> w25q128fw) when using ioctl(MEMERASE) with offset=0 and length=16M. The
> input parameters matter because spi_nor_erase() uses a different code
> path for full-chip erase, where we use the SPINOR_OP_CHIP_ERASE (0xc7)
> opcode.
> 
> Fix: use a different timeout for full-chip erase than for other
> commands.
> 
> While most operations can be expected to perform relatively similarly
> across a variety of NOR flash types and sizes (and therefore might as
> well use a similar timeout to keep things simple), full-chip erase is
> unique, because the time it typically takes to complete:
> (1) is much larger than most operations and
> (2) scales with the size of the flash.
> 
> Let's base our timeout on the original comments stuck here -- that a 2MB
> flash requires max 40s to erase.
> 
> Small survey of a few flash datasheets I have lying around:
> 
>   Chip         Size (MB)   Max chip erase (seconds)
>   ----         --------    ------------------------
>   w25q32fw     4           50
>   w25q64cv     8           30
>   w25q64fw     8           100
>   w25q128fw    16          200
>   s25fl128s    16          ~256
>   s25fl256s    32          ~512
> 
> From this data, it seems plenty sufficient to say we need to wait for
> 40 seconds for each 2MB of flash.
> 
> After this change, it might make some sense to decrease the timeout for
> everything else, as even the most extreme operations (single block
> erase?) shouldn't take more than a handful of seconds. But for safety,
> let's leave it as-is. It's only an error case, after all, so we don't
> exactly need to optimize it.
> 
> Signed-off-by: Furquan Shaikh <furquan@google.com>
> Signed-off-by: Brian Norris <computersforpeace@gmail.com>

Pushed to l2-mtd.git