Messages in this thread | | | Subject | Re: [PATCH 3/3] bus: mhi: core: Remove link_status() callback | From | Jeffrey Hugo <> | Date | Tue, 7 Apr 2020 09:03:28 -0600 |
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On 4/6/2020 11:58 PM, Manivannan Sadhasivam wrote: > Hi Jeff, > > On Mon, Apr 06, 2020 at 03:04:37PM -0600, Jeffrey Hugo wrote: >> 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> > > LGTM. But as per the IRC discussion I'd like the mhi_reg_read() to be > implemented as a callback in mhi_controller struct inorder to truly make MHI > a PCI agnostic bus. > > Since we don't have any controller driver in mainline, I think it is the > good time to do this change.
No problem. I thought you might prefer that approach, hence the discussion. :)
Do you want that included in this change, or as a follow up?
> > For this, > > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> > > Thanks, > Mani > >> --- >> drivers/bus/mhi/core/init.c | 6 ++---- >> drivers/bus/mhi/core/main.c | 5 ++--- >> include/linux/mhi.h | 2 -- >> 3 files changed, 4 insertions(+), 9 deletions(-) >> >> diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c >> index b38359c..2af08d57 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 eb4256b..473278b8 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; >> diff --git a/include/linux/mhi.h b/include/linux/mhi.h >> index ad19960..be704a4 100644 >> --- a/include/linux/mhi.h >> +++ b/include/linux/mhi.h >> @@ -335,7 +335,6 @@ struct mhi_controller_config { >> * @syserr_worker: System error worker >> * @state_event: State change event >> * @status_cb: CB function to notify power states of the device (required) >> - * @link_status: CB function to query link status of the device (required) >> * @wake_get: CB function to assert device wake (optional) >> * @wake_put: CB function to de-assert device wake (optional) >> * @wake_toggle: CB function to assert and de-assert device wake (optional) >> @@ -417,7 +416,6 @@ struct mhi_controller { >> >> void (*status_cb)(struct mhi_controller *mhi_cntrl, >> enum mhi_callback cb); >> - int (*link_status)(struct mhi_controller *mhi_cntrl); >> void (*wake_get)(struct mhi_controller *mhi_cntrl, bool override); >> void (*wake_put)(struct mhi_controller *mhi_cntrl, bool override); >> void (*wake_toggle)(struct mhi_controller *mhi_cntrl); >> -- >> Qualcomm Technologies, Inc. is a member of the >> Code Aurora Forum, a Linux Foundation Collaborative Project.
-- Jeffrey Hugo Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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