Re: xHCI problem? [was Re: Erratic USB device behavior and device loss]

Alan Stern
2016-09-07T20:48:55Z

On Tue, 6 Sep 2016, Ulf Hansson wrote:

> On 5 September 2016 at 17:58, Alan Stern <stern-nwvwT67g6+6dFdvTe/nMLpVzexx5G7lz@public.gmane.org> wrote:
> > On Mon, 5 Sep 2016, Ritesh Raj Sarraf wrote:
> >
> >> -----BEGIN PGP SIGNED MESSAGE-----
> >> Hash: SHA512
> >>
> >> On Sun, 2016-09-04 at 15:46 -0400, Alan Stern wrote:
> >> >
> >> > This is not the problem I was discussing with Ulf. The problem was why
> >> > the device kept going into and out of runtime suspend every three
> >> > seconds. The kernel log above does not say whether this was happening.
> >> > One way to tell is to look at a usbmon trace (like we did before).
> >>
> >> https://people.debian.org/~rrs/tmp/usbmon.txt.gz
> >>
> >> This should have the logs you asked for, running on 4.8-rc4.
> >
> > Confirmed, the runtime suspends and resumes are still happening.
> >
> > Ulf, any insights?
>
> Alan, Ritesh,
>
> Yes, I am starting to understand more about what goes on here.
> Although I need help to test as I don't have the HW.
> As you already guessed, I suspect the problem is within the runtime PM
> deployment in the drivers/mmc/host/rtsx_usb_sdmmc.c.
>
> Let me start by first give you some background to how the mmc core
> deals with runtime PM.
>
> *)
> The mmc core manages most of the calls to the pm_runtime_get|put*()
> and pm_runtime_mark_last_busy() for the mmc host device. The gets/puts
> are done when the core is about to access the mmc host device, via the
> mmc host ops driver interface. You may search for calls to the
> mmc_claim|release_host() functions to find out when the gets/puts are
> done.

Since mmc_claim_host() does call pm_runtime_get_sync(), these runtime
suspends would not occur if the host was claimed. So we can conclude
that rtsx_usb_sdmmc.c must be doing I/O to the device without claiming
the host.

> **)
> The mmc core have also deployed runtime PM for the mmc *card* device
> and which has the runtime PM autosuspend feature enabled with a 3s
> default timeout. One important point is that the mmc card device has
> the mmc host device assigned as being its parent device. I guessing
> the reason to why you are encountering strange 3s intervals of runtime
> PM suspend/resume is related to this.

That sounds likely.

> Now, in this case, the rtsx_usb_sdmmc driver seems to need a bit of
> special runtime PM deployment, as the calls to pm_runtime_get|put*()
> also controls the power to the usb device and thus also the power to
> the card. I am guessing that's done via the usb device being assigned
> as parent for the mmc host's platform device!?

Yes, in drivers/mfd/mfd-core.c's mfd_add_device() routine, which is
called indirectly by drivers/mfd/rtsx_usb.c's probe routine.

> By reviewing the code of the rtsx_usb_sdmmc driver, particularly how
> it calls pm_runtime_get|put() I am guessing those calls may not be
> properly deployed. Perhaps rtsx_usb_sdmmc should convert to use the
> usb_autopm_put|get_interface() and friends, although I didn't want to
> make that change at this point so instead I have cooked a patch that
> might fixes the behaviour.

The usb_autopm_* calls are mostly just convenience wrappers around the
pm_runtime_* functions, meant for use with USB drivers. In fact, you
can't use them with a platform_device.

It seems odd that rtsx_usb_sdmmc calls pm_runtime_put() and
pm_runtime_get_sync() directly instead of using
mmc_claim|release_host().

> Ritesh, can you please try it out to see what happens?
>
> ---
> drivers/mmc/host/rtsx_usb_sdmmc.c | 7 +------
> 1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/drivers/mmc/host/rtsx_usb_sdmmc.c
> b/drivers/mmc/host/rtsx_usb_sdmmc.c
> index 6c71fc9..3d6fe51 100644
> --- a/drivers/mmc/host/rtsx_usb_sdmmc.c
> +++ b/drivers/mmc/host/rtsx_usb_sdmmc.c
> @@ -1138,11 +1138,6 @@ static void sdmmc_set_ios(struct mmc_host *mmc,
> struct mmc_ios *ios)
> dev_dbg(sdmmc_dev(host), "%s\n", __func__);
> mutex_lock(&ucr->dev_mutex);
>
> - if (rtsx_usb_card_exclusive_check(ucr, RTSX_USB_SD_CARD)) {
> - mutex_unlock(&ucr->dev_mutex);
> - return;
> - }
> -
> sd_set_power_mode(host, ios->power_mode);
> sd_set_bus_width(host, ios->bus_width);
> sd_set_timing(host, ios->timing, &host->ddr_mode);
> @@ -1336,7 +1331,7 @@ static void rtsx_usb_init_host(struct
> rtsx_usb_sdmmc *host)
> MMC_CAP_MMC_HIGHSPEED | MMC_CAP_BUS_WIDTH_TEST |
> MMC_CAP_UHS_SDR12 | MMC_CAP_UHS_SDR25 | MMC_CAP_UHS_SDR50 |
> MMC_CAP_NEEDS_POLL;
> - mmc->caps2 = MMC_CAP2_NO_PRESCAN_POWERUP | MMC_CAP2_FULL_PWR_CYCLE;
> + mmc->caps2 = MMC_CAP2_FULL_PWR_CYCLE;
>
> mmc->max_current_330 = 400;
> mmc->max_current_180 = 800;

These changes don't seem to affect the way rtsx_usb_sdmmc.c handles
runtime PM. In particular, the driver doesn't call
pm_runtime_mark_last_busy() anywhere.

Alan Stern