Hi Shubhrajyoti, On 03/28/12 12:03, Shubhrajyoti wrote: > On Tuesday 27 March 2012 07:38 PM, Igor Grinberg wrote: >> When PHY reset pin is connected to a GPIO on external GPIO chip >> (e.g. I2C), we should not call the gpio_set_value() function, but >> gpio_set_value_cansleep(). > Why so ? Whats the error otherwise ? Otherwise, we get a very confusing warnings: WARNING: at /home/grinberg/git-repo/linux-omap/drivers/gpio/gpiolib.c:1584 __gpio_set_value+0x5c/0x64() Modules linked in: [<c001ae6c>] (unwind_backtrace+0x0/0xfc) from [<c003ba10>] (warn_slowpath_common+0x54/0x64) [<c003ba10>] (warn_slowpath_common+0x54/0x64) from [<c003ba3c>] (warn_slowpath_null+0x1c/0x24) [<c003ba3c>] (warn_slowpath_null+0x1c/0x24) from [<c0260860>] (__gpio_set_value+0x5c/0x64) [<c0260860>] (__gpio_set_value+0x5c/0x64) from [<c035fde8>] (ehci_hcd_omap_probe+0x390/0x6c0) [<c035fde8>] (ehci_hcd_omap_probe+0x390/0x6c0) from [<c02d59dc>] (platform_drv_probe+0x18/0x1c) [<c02d59dc>] (platform_drv_probe+0x18/0x1c) from [<c02d44d0>] (really_probe+0x64/0x160) [<c02d44d0>] (really_probe+0x64/0x160) from [<c02d4614>] (driver_probe_device+0x48/0x60) [<c02d4614>] (driver_probe_device+0x48/0x60) from [<c02d46c0>] (__driver_attach+0x94/0x98) [<c02d46c0>] (__driver_attach+0x94/0x98) from [<c02d2f4c>] (bus_for_each_dev+0x54/0x80) [<c02d2f4c>] (bus_for_each_dev+0x54/0x80) from [<c02d3680>] (bus_add_driver+0xa8/0x2a4) [<c02d3680>] (bus_add_driver+0xa8/0x2a4) from [<c02d4cbc>] (driver_register+0x78/0x184) [<c02d4cbc>] (driver_register+0x78/0x184) from [<c062e744>] (ehci_hcd_init+0xd8/0x114) [<c062e744>] (ehci_hcd_init+0xd8/0x114) from [<c0008758>] (do_one_initcall+0x34/0x184) [<c0008758>] (do_one_initcall+0x34/0x184) from [<c0612248>] (do_basic_setup+0x34/0x40) [<c0612248>] (do_basic_setup+0x34/0x40) from [<c06122b8>] (kernel_init+0x64/0xec) [<c06122b8>] (kernel_init+0x64/0xec) from [<c00154cc>] (kernel_thread_exit+0x0/0x8) ---[ end trace 1b75b31a2719ed1e ]--- Because GPIOs can be used from atomic context, there are two versions of GPIO control functions: gpio_<set|get>_value() and gpio_<set|get>_value_cansleep(). The warning above means that the atomic context safe function has been called, but the GPIO chip is not atomic safe - requires an I2C transaction which may sleep and therefore a warning. Now, for all on SoC GPIOs, the time for the gpio_set_value_cansleep() call should not be different then the one for the gpio_set_value(). After my patch, the behavior should not change, but eliminate the warning for external GPIO chip users. >> Signed-off-by: Igor Grinberg <grinberg@xxxxxxxxxxxxxx> >> --- >> This patch depends on the patch from Keshava [1]: >> ARM: OMAP3: USB: Fix the EHCI ULPI PHY reset issue >> >> [1] http://www.spinics.net/lists/linux-omap/msg66774.html >> >> drivers/usb/host/ehci-omap.c | 4 ++-- >> 1 files changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/usb/host/ehci-omap.c b/drivers/usb/host/ehci-omap.c >> index 5c78f9e..26e9241 100644 >> --- a/drivers/usb/host/ehci-omap.c >> +++ b/drivers/usb/host/ehci-omap.c >> @@ -258,10 +258,10 @@ static int ehci_hcd_omap_probe(struct platform_device *pdev) >> udelay(10); >> >> if (gpio_is_valid(pdata->reset_gpio_port[0])) >> - gpio_set_value(pdata->reset_gpio_port[0], 1); >> + gpio_set_value_cansleep(pdata->reset_gpio_port[0], 1); >> >> if (gpio_is_valid(pdata->reset_gpio_port[1])) >> - gpio_set_value(pdata->reset_gpio_port[1], 1); >> + gpio_set_value_cansleep(pdata->reset_gpio_port[1], 1); >> } >> >> return 0; > > -- Regards, Igor. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
