[PATCH 4/7] mtd: spi-nor: fsl-quadspi: i.MX6SX: fixed the random QSPI access failed issue

[Brian Norris]

On Wed, Jul 22, 2015 at 03:39:56AM +0800, Frank.Li at freescale.com wrote:
> From: Allen Xu <b45815 at freescale.com>
> 
> We found there is a low probability(5%) QSPI access timeout issue,
> usually it happened on kernel boot stage, the first time kernel tried to
> access QSPI chip. The READ_ID command was sent but not executed,
> consequently the probe function failed.
> 
> Finally we located the issue by these steps.
> 
> 1. Since the issue happened randomly and usually it cost half day to
> reproduce, we add more debug code in driver, to create a timeout file if
> the issue occurred.
> 
> 2. Prepared an autorun script to keep rebooting the system and check if
> the timeout file existed, if the file existed, stop reboot.
> 
> 3. The system will stop rebooting when timeout error occurred, set the
> CCM_CCOSR register and related IOMUX to measure QPSI clock, found there
> is no clock output, while clock output can be measured when QSPI driver
> successfully probed.
> 
> 4. Check the code and found QSPI clock rate was changed while not
> disabled clock gate, most of the multiplexers on i.MX6 are glitch ones,
> clock glitch may occurred and propagated into downstream clock dividers
> 
> Based on the new clock flag(CLK_SET_RATE_GATE) and new framework, we
> need to change the approach of seting clock rate. In current
> implementation, there are several places in which the clock was touched.
> 
> 1. probe function. prepare and enable clock before setting the QSPI
> register, disable and unprepare the clock before exit.
> 
> 2. nor_setup & nor_setup_last, since we change clock rate in these two
> functions.
> 
> 3. fsl_qspi_prep and fsl_qspi_unprep, clock was enabled only when got
> QSPI access request.
> 
> 4. resume function. Clock was required to restroe the setting after
> resume, disable the clock before exit.
> 
> Signed-off-by: Allen Xu <b45815 at freescale.com>
> Signed-off-by: Frank Li <Frank.Li at freescale.com>
> ---
>  drivers/mtd/spi-nor/fsl-quadspi.c | 83 +++++++++++++++++++++++++++------------
>  1 file changed, 58 insertions(+), 25 deletions(-)

[...]

This patch does not apply to l2-mtd.git.