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[v2,0/4] renesas_sdhi: fix hang when SCC loses its clock

Message ID 20200901150250.26236-1-wsa+renesas@sang-engineering.com
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Series renesas_sdhi: fix hang when SCC loses its clock | expand

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Wolfram Sang Sept. 1, 2020, 3:02 p.m. UTC 
This again took a while since v1 because the issue was so hard to
trigger. But I finally found a way to inject the flaw, so this series
could be tested and it fixes the issue.

Changes since v1:
	* introduce a new flag to MMC core indicating any kind of tuning
	  not only retune
	* use the new flag to keep SCC flag active
	* new patch 4, minor cleanup to MMC core

A branch including the DEBUG patch can be found here:

git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git renesas/sdhi/new_manual_calib-for-5.10

If you revert patch 3, you should have the SCC hang during boot again.
For the record, let me copy some findings I mentioned in another thread:

===
Interesting news: The hang comes from a code path I would have not
expected. It is not because of accessing an SCC register, it is this
line from renesas_sdhi_set_clock() which causes the issue:

186         sd_ctrl_write16(host, CTL_SD_CARD_CLK_CTL, clk & CLK_CTL_DIV_MASK);

I mean I can guess that the clock setting has something to do with the
SCC, but I can't see the direct connection with the documentation I
have.
===

Tested on R-Car H3 ES2.0 and M3-N and patches based on mmc/next.

Another hope this is gone for good now...

Kind regards,

   Wolfram


Wolfram Sang (4):
  mmc: core: when downgrading HS400, callback into drivers earlier
  mmc: core: add a 'doing_init_tune' flag and a 'mmc_doing_tune' helper
  mmc: renesas_sdhi: keep SCC clock active when tuning
  mmc: core: simplify an expression

 drivers/mmc/core/mmc.c               | 16 ++++++++++------
 drivers/mmc/host/renesas_sdhi_core.c |  8 ++++++--
 include/linux/mmc/host.h             |  6 ++++++
 3 files changed, 22 insertions(+), 8 deletions(-)