From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [PATCH v3 04/15] clocksource: Add ARM System timer driver Date: Fri, 27 Mar 2015 09:36:37 +0100 Message-ID: <55151695.5050203@linaro.org> References: <1426197361-19290-1-git-send-email-maxime.coquelin@st.com> <1426197361-19290-5-git-send-email-maxime.coquelin@st.com> <5513D64A.7060702@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail-wi0-f170.google.com ([209.85.212.170]:37342 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753377AbbC0Ign (ORCPT ); Fri, 27 Mar 2015 04:36:43 -0400 Received: by wiaa2 with SMTP id a2so21238663wia.0 for ; Fri, 27 Mar 2015 01:36:42 -0700 (PDT) In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Maxime Coquelin Cc: =?UTF-8?B?VXdlIEtsZWluZS1Lw7ZuaWc=?= , =?UTF-8?B?QW5kcmVhcyBGw6RyYmVy?= , Geert Uytterhoeven , Rob Herring , Philipp Zabel , Linus Walleij , Arnd Bergmann , Stefan Agner , Peter Meerwald , Paul Bolle , Jonathan Corbet , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Russell King , Thomas Gleixner , Greg Kroah-Hartman , Jiri Slaby , Andrew Morton , "David S. Miller" , Mauro Carvalho Chehab On 03/26/2015 09:19 PM, Maxime Coquelin wrote: > Hi Daniel, > > Thanks for the review. Please find my answers below. > > 2015-03-26 10:50 GMT+01:00 Daniel Lezcano = : >> On 03/12/2015 10:55 PM, Maxime Coquelin wrote: >>> >>> From: Maxime Coquelin >>> >>> This patch adds clocksource support for ARMv7-M's System timer, >>> also known as SysTick. >>> >>> Signed-off-by: Maxime Coquelin >> >> >> Hi Maxime, >> >> the driver looks good. Three comments below. >> >> -- Daniel >> >> [ ... ] >>> +static void __init system_timer_of_register(struct device_node *np= ) >>> +{ >>> + struct clk *clk; >>> + void __iomem *base; >>> + u32 rate =3D 0; >>> + int ret; >>> + >>> + base =3D of_iomap(np, 0); >>> + if (!base) { >>> + pr_warn("system-timer: invalid base address\n"); >>> + return; >>> + } >>> + >>> + clk =3D of_clk_get(np, 0); >>> + if (!IS_ERR(clk)) { >>> + ret =3D clk_prepare_enable(clk); >>> + if (ret) { >>> + clk_put(clk); >>> + goto out_unmap; >>> + } >>> + >>> + rate =3D clk_get_rate(clk); >>> + } >>> + >>> + /* If no clock found, try to get clock-frequency property *= / >>> + if (!rate) { >>> + ret =3D of_property_read_u32(np, "clock-frequency",= &rate); >>> + if (ret) >>> + goto out_unmap; >> >> >> Shouldn't be 'goto out_clk_disable' ? > > No, because I assumed !rate means we failed to get the clock. > Actually, clk_get_rate could return 0, so relying on rate value is no= t safe. > > I propose to get clock-frequency property if IS_ERR(clk). > > Is it fine for you? Why not invert the conditions ? If the 'clock-frequency' is specified i= n=20 the DT then it overrides the clk_get_rate(). So the resulting code will= be: ret =3D of_property_read_u32(np, "clock-frequency", &rate); if (ret) { clk =3D of_clk_get(np, 0); if (IS_ERR(clk)) goto out_unmap; ret =3D clk_prepare_enable(clk); if (ret) goto out_clk_put; rate =3D clk_get_rate(clk); if (!rate) goto out_clk_unprepare; } >>> + } >>> + >>> + writel_relaxed(SYSTICK_LOAD_RELOAD_MASK, base + SYST_RVR); >>> + writel_relaxed(SYST_CSR_ENABLE, base + SYST_CSR); >>> + >>> + ret =3D clocksource_mmio_init(base + SYST_CVR, "arm_system_= timer", >>> rate, >>> + 200, 24, clocksource_mmio_readl_down); >>> + if (ret) { >>> + pr_err("failed to init clocksource (%d)\n", ret); >>> + goto out_clk_disable; >>> + } >>> + >>> + pr_info("ARM System timer initialized as clocksource\n"); >>> + >>> + return; >>> + >>> +out_clk_disable: >>> + if (!IS_ERR(clk)) >> >> >> Why do you need this check ? > > To handle the case were no clock was found, but a clk-frequency value > was provided. > >> >> It isn't missing a clk_put ? > > Right, thanks for spotting this. > > I wonder if it makes sense to implement the error path. > If we fail to initialize the clocksource, the system will be unusable= =2E > > Maybe I should just perform a BUG_ON() in the error cases, as most of > the other clocksource drivers do. > What is your view? I prefer to not BUG_ON in the init functions because it already happen=20 that drivers were bugging at init time and when a driver was reused on=20 another platform with several timers available, the board was not able=20 to boot because one timer was not used, hence not defined in the DT. I=20 don't know if that could be the case for this platform but I prefer to=20 keep thing going smoothly and return from init even if that lead to a=20 kernel hang. Of course, the errors must be displayed (pr_warn, pr_err,=20 pr_notice, etc ...). >> >>> + clk_disable_unprepare(clk); >>> +out_unmap: >>> + iounmap(base); >>> + WARN(ret, "ARM System timer register failed (%d)\n", ret); pr_warn Thanks -- Daniel --=20 Linaro.org =E2=94=82 Open source software fo= r ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f170.google.com ([209.85.212.170]:37342 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753377AbbC0Ign (ORCPT ); Fri, 27 Mar 2015 04:36:43 -0400 Received: by wiaa2 with SMTP id a2so21238663wia.0 for ; Fri, 27 Mar 2015 01:36:42 -0700 (PDT) Message-ID: <55151695.5050203@linaro.org> Date: Fri, 27 Mar 2015 09:36:37 +0100 From: Daniel Lezcano MIME-Version: 1.0 Subject: Re: [PATCH v3 04/15] clocksource: Add ARM System timer driver References: <1426197361-19290-1-git-send-email-maxime.coquelin@st.com> <1426197361-19290-5-git-send-email-maxime.coquelin@st.com> <5513D64A.7060702@linaro.org> In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Maxime Coquelin Cc: =?UTF-8?B?VXdlIEtsZWluZS1Lw7ZuaWc=?= , =?UTF-8?B?QW5kcmVhcyBGw6RyYmVy?= , Geert Uytterhoeven , Rob Herring , Philipp Zabel , Linus Walleij , Arnd Bergmann , Stefan Agner , Peter Meerwald , Paul Bolle , Jonathan Corbet , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Russell King , Thomas Gleixner , Greg Kroah-Hartman , Jiri Slaby , Andrew Morton , "David S. Miller" , Mauro Carvalho Chehab , Joe Perches , Antti Palosaari , Tejun Heo , Will Deacon , Nikolay Borisov , Rusty Russell , Kees Cook , Michal Marek , "linux-doc@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "devicetree@vger.kernel.org" , "linux-gpio@vger.kernel.org" , "linux-serial@vger.kernel.org" , Linux-Arch , "linux-api@vger.kernel.org" Message-ID: <20150327083637.ln4fvQDuUfoUTuKxDtKUVA_zbMEMsWI7FVS80PFaxEU@z> On 03/26/2015 09:19 PM, Maxime Coquelin wrote: > Hi Daniel, > > Thanks for the review. Please find my answers below. > > 2015-03-26 10:50 GMT+01:00 Daniel Lezcano : >> On 03/12/2015 10:55 PM, Maxime Coquelin wrote: >>> >>> From: Maxime Coquelin >>> >>> This patch adds clocksource support for ARMv7-M's System timer, >>> also known as SysTick. >>> >>> Signed-off-by: Maxime Coquelin >> >> >> Hi Maxime, >> >> the driver looks good. Three comments below. >> >> -- Daniel >> >> [ ... ] >>> +static void __init system_timer_of_register(struct device_node *np) >>> +{ >>> + struct clk *clk; >>> + void __iomem *base; >>> + u32 rate = 0; >>> + int ret; >>> + >>> + base = of_iomap(np, 0); >>> + if (!base) { >>> + pr_warn("system-timer: invalid base address\n"); >>> + return; >>> + } >>> + >>> + clk = of_clk_get(np, 0); >>> + if (!IS_ERR(clk)) { >>> + ret = clk_prepare_enable(clk); >>> + if (ret) { >>> + clk_put(clk); >>> + goto out_unmap; >>> + } >>> + >>> + rate = clk_get_rate(clk); >>> + } >>> + >>> + /* If no clock found, try to get clock-frequency property */ >>> + if (!rate) { >>> + ret = of_property_read_u32(np, "clock-frequency", &rate); >>> + if (ret) >>> + goto out_unmap; >> >> >> Shouldn't be 'goto out_clk_disable' ? > > No, because I assumed !rate means we failed to get the clock. > Actually, clk_get_rate could return 0, so relying on rate value is not safe. > > I propose to get clock-frequency property if IS_ERR(clk). > > Is it fine for you? Why not invert the conditions ? If the 'clock-frequency' is specified in the DT then it overrides the clk_get_rate(). So the resulting code will be: ret = of_property_read_u32(np, "clock-frequency", &rate); if (ret) { clk = of_clk_get(np, 0); if (IS_ERR(clk)) goto out_unmap; ret = clk_prepare_enable(clk); if (ret) goto out_clk_put; rate = clk_get_rate(clk); if (!rate) goto out_clk_unprepare; } >>> + } >>> + >>> + writel_relaxed(SYSTICK_LOAD_RELOAD_MASK, base + SYST_RVR); >>> + writel_relaxed(SYST_CSR_ENABLE, base + SYST_CSR); >>> + >>> + ret = clocksource_mmio_init(base + SYST_CVR, "arm_system_timer", >>> rate, >>> + 200, 24, clocksource_mmio_readl_down); >>> + if (ret) { >>> + pr_err("failed to init clocksource (%d)\n", ret); >>> + goto out_clk_disable; >>> + } >>> + >>> + pr_info("ARM System timer initialized as clocksource\n"); >>> + >>> + return; >>> + >>> +out_clk_disable: >>> + if (!IS_ERR(clk)) >> >> >> Why do you need this check ? > > To handle the case were no clock was found, but a clk-frequency value > was provided. > >> >> It isn't missing a clk_put ? > > Right, thanks for spotting this. > > I wonder if it makes sense to implement the error path. > If we fail to initialize the clocksource, the system will be unusable. > > Maybe I should just perform a BUG_ON() in the error cases, as most of > the other clocksource drivers do. > What is your view? I prefer to not BUG_ON in the init functions because it already happen that drivers were bugging at init time and when a driver was reused on another platform with several timers available, the board was not able to boot because one timer was not used, hence not defined in the DT. I don't know if that could be the case for this platform but I prefer to keep thing going smoothly and return from init even if that lead to a kernel hang. Of course, the errors must be displayed (pr_warn, pr_err, pr_notice, etc ...). >> >>> + clk_disable_unprepare(clk); >>> +out_unmap: >>> + iounmap(base); >>> + WARN(ret, "ARM System timer register failed (%d)\n", ret); pr_warn Thanks -- Daniel -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog