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| author | Jeffrey Hugo <jhugo@codeaurora.org> | 2020-05-01 00:35:52 +0530 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-05-05 16:58:35 +0200 |
| commit | 85a087df4a719ebab940efa3c79625e68161f57b (patch) | |
| tree | 8996987fe824d700f99b05d4211412a492ce8903 /drivers/bus | |
| parent | ce312258084ea0c828e11c831c7b9e8b42b02ef8 (diff) | |
| download | linux-85a087df4a719ebab940efa3c79625e68161f57b.tar.gz linux-85a087df4a719ebab940efa3c79625e68161f57b.tar.bz2 linux-85a087df4a719ebab940efa3c79625e68161f57b.zip | |
bus: mhi: core: Remove link_status() callback
If the MHI core detects invalid data due to a PCI read, it calls into
the controller via link_status() to double check that the link is infact
down. All in all, this is pretty pointless, and racy. There are no good
reasons for this, and only drawbacks.
Its pointless because chances are, the controller is going to do the same
thing to determine if the link is down - attempt a PCI access and compare
the result. This does not make the link status decision any smarter.
Its racy because its possible that the link was down at the time of the
MHI core access, but then recovered before the controller access. In this
case, the controller will indicate the link is not down, and the MHI core
will precede to use a bad value as the MHI core does not attempt to retry
the access.
Retrying the access in the MHI core is a bad idea because again, it is
racy - what if the link is down again? Furthermore, there may be some
higher level state associated with the link status, that is now invalid
because the link went down.
The only reason why the MHI core could see "invalid" data when doing a PCI
access, that is actually valid, is if the register actually contained the
PCI spec defined sentinel for an invalid access. In this case, it is
arguable that the MHI implementation broken, and should be fixed, not
worked around.
Therefore, remove the link_status() callback before anyone attempts to
implement it.
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Hemant Kumar <hemantk@codeaurora.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20200430190555.32741-4-manivannan.sadhasivam@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/bus')
| -rw-r--r-- | drivers/bus/mhi/core/init.c | 6 | ||||
| -rw-r--r-- | drivers/bus/mhi/core/main.c | 5 |
2 files changed, 4 insertions, 7 deletions
diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c index b38359c480ea..2af08d57ec28 100644 --- a/drivers/bus/mhi/core/init.c +++ b/drivers/bus/mhi/core/init.c @@ -812,10 +812,8 @@ int mhi_register_controller(struct mhi_controller *mhi_cntrl, if (!mhi_cntrl) return -EINVAL; - if (!mhi_cntrl->runtime_get || !mhi_cntrl->runtime_put) - return -EINVAL; - - if (!mhi_cntrl->status_cb || !mhi_cntrl->link_status) + if (!mhi_cntrl->runtime_get || !mhi_cntrl->runtime_put || + !mhi_cntrl->status_cb) return -EINVAL; ret = parse_config(mhi_cntrl, config); diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c index 55928feea0c9..f8401535e61a 100644 --- a/drivers/bus/mhi/core/main.c +++ b/drivers/bus/mhi/core/main.c @@ -20,9 +20,8 @@ int __must_check mhi_read_reg(struct mhi_controller *mhi_cntrl, { u32 tmp = readl(base + offset); - /* If there is any unexpected value, query the link status */ - if (PCI_INVALID_READ(tmp) && - mhi_cntrl->link_status(mhi_cntrl)) + /* If the value is invalid, the link is down */ + if (PCI_INVALID_READ(tmp)) return -EIO; *out = tmp; |