From: khilman@ti.com (Kevin Hilman) Date: Thu, 13 Oct 2011 14:22:13 -0700 Subject: [PATCH v6 09/16] OMAP2+: UART: Add runtime pm support for omap-serial driver In-Reply-To: (Govindraj's message of "Thu, 13 Oct 2011 06:58:48 +0530") References: <1317380495-584-1-git-send-email-govindraj.raja@ti.com> <1317380495-584-9-git-send-email-govindraj.raja@ti.com> <878voplppo.fsf@ti.com> Message-ID: <87obxkio3e.fsf@ti.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Govindraj writes: > On Thu, Oct 13, 2011 at 5:36 AM, Kevin Hilman wrote: >> "Govindraj.R" writes: >> >> [...] >> >>> Use device_may_wakeup to check whether uart has wakeup capabilities >>> and then enable uart runtime usage for the uart. >> >> Curious about what happens when device_may_wakeup() is not set during >> device init. >> >> [...] >> >>> @@ -1305,6 +1363,16 @@ static int serial_omap_probe(struct platform_device *pdev) >>> ? ? ? ? ? ? ? up->uart_dma.rx_dma_channel = OMAP_UART_DMA_CH_FREE; >>> ? ? ? } >>> >>> + ? ? pm_runtime_use_autosuspend(&pdev->dev); >>> + ? ? pm_runtime_set_autosuspend_delay(&pdev->dev, >>> + ? ? ? ? ? ? ? ? ? ? OMAP_UART_AUTOSUSPEND_DELAY); >>> + >>> + ? ? pm_runtime_irq_safe(&pdev->dev); >>> + ? ? if (device_may_wakeup(&pdev->dev)) { >>> + ? ? ? ? ? ? pm_runtime_enable(&pdev->dev); >> >> So if device_may_wakeup() is false, runtime PM is not enabled, then... >> >>> + ? ? ? ? ? ? pm_runtime_get_sync(&pdev->dev); >> >> ...this get doesn't happen, and the first register access causes a crash. > > Actually no crash, clocks will left enabled from boot up (hwmod_no_reset/idle) > that are idled and enabled back here. > > Since hwmod_idle is binded here later ([PATCH v6 15/16]), IMO, That's not a very maintainable solution. What happens when when someone fixes serial.c to only set HWMOD_INIT_NO_IDLE on the console UART? or if we fix things so we don't need INIT_NO_IDLE anymore? Then this will crash. Driver code should not make assumptions like this about what device init code is or isn't doing. Kevin