[PATCH] mtd: rawnand: nandsim: Artificially prevent sequential page reads

[Miquel Raynal]

On Fri, 2023-03-10 at 08:54:52 UTC, Miquel Raynal wrote:
> The continuous read support added recently makes nandsim
> unhappy. Indeed, all the supported commands should be re-encoded into
> internal commands, so of course there is currently no support for the
> commands and patterns needed for continuous reads to work.
> 
> I tried to add support for them but nandsim (which is more a tool to
> develop/debug upper layers rather than the raw NAND core) suffers from a
> big limitation: it's internal parser needs to know what exact operation
> is happening when the address cycles are performed. The research is then
> sequential from the start up to the address cycles, but does not check
> what's coming next even though the information is available. This is a
> limitation which is related to the old API used by the core which kind
> of forced the controllers to guess what operation was being performed
> rather early. Today the core uses a more transparent API called
> ->exec_op() which no longer requires controller drivers to do any more
> guessing, but despite being updated to ->exec_op(), nandsim is still a
> bit constrained on this regard and thus cannot handle sequential page
> reads because the start sequence beginning is identical to a regular
> page read.
> 
> If the internal algorithm is updated some day, it should be possible to
> make it support sequential page reads by adding something like:
> 
>        /* Large page devices continuous read page start */
>        {OPT_LARGEPAGE, {STATE_CMD_READ0, STATE_ADDR_PAGE, STATE_CMD_READSTART,
>                         STATE_CMD_READCACHESEQ | ACTION_CPY, STATE_DATAOUT,
>                         STATE_READY}},
>        /* Large page devices continuous read page continue */
>        {OPT_LARGEPAGE, {STATE_CMD_READCACHESEQ | ACTION_CPY_NEXT, STATE_DATAOUT,
>                         STATE_READY}},
>        /* Large page devices continuous read page end */
>        {OPT_LARGEPAGE, {STATE_CMD_READCACHEEND | ACTION_CPY_NEXT, STATE_DATAOUT,
>                         STATE_READY}},
> 
> For now, we just return -EOPNOTSUPP when the core asks controller
> drivers if they support the feature in order to prevent any further use
> of these opcodes.
> 
> Note: This is a hack, ->exec_op() is not supposed to check against the
> COMMAND opcodes unless _really_ needed.
> 
> Fixes: 003fe4b9545b ("mtd: rawnand: Support for sequential cache reads")
> Reported-by: Zhihao Cheng <chengzhihao1 at huawei.com>
> Link: https://lore.kernel.org/linux-mtd/fd34fe55-7f4a-030d-8653-9bb9cf08410d@huawei.com/
> Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
> Tested-by: Zhihao Cheng <chengzhihao1 at huawei.com>
> Acked-by: Richard Weinberger <richard at nod.at>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes.

Miquel