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Wed, 29 Jul 2020 07:55:08 -0700 (PDT) Subject: Re: [PATCH V2 1/2] watchdog: imx7ulp: Strictly follow the sequence for wdog operations To: Anson Huang , "wim@linux-watchdog.org" , "shawnguo@kernel.org" , "s.hauer@pengutronix.de" , "kernel@pengutronix.de" , "festevam@gmail.com" , "linux-watchdog@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Cc: dl-linux-imx References: <1595989227-24700-1-git-send-email-Anson.Huang@nxp.com> <00587a78-8069-4fbd-7e02-b774d541f75a@roeck-us.net> From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+ J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q= Message-ID: <22e16ed3-355a-70c4-ccc7-aece498b29fb@roeck-us.net> Date: Wed, 29 Jul 2020 07:55:06 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-watchdog-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-watchdog@vger.kernel.org On 7/28/20 10:02 PM, Anson Huang wrote: > Hi, Guenter > > >> Subject: RE: [PATCH V2 1/2] watchdog: imx7ulp: Strictly follow the sequence >> for wdog operations >> >> Hi, Guenter >> >> >>> Subject: Re: [PATCH V2 1/2] watchdog: imx7ulp: Strictly follow the >>> sequence for wdog operations >>> >>> On 7/28/20 7:20 PM, Anson Huang wrote: >>>> According to reference manual, the i.MX7ULP WDOG's operations should >>>> follow below sequence: >>>> >>>> 1. disable global interrupts; >>>> 2. unlock the wdog and wait unlock bit set; 3. reconfigure the wdog >>>> and wait for reconfiguration bit set; 4. enabel global interrupts. >>>> >>>> Strictly follow the recommended sequence can make it more robust. >>>> >>>> Signed-off-by: Anson Huang >>>> --- >>>> Changes since V1: >>>> - use readl_poll_timeout_atomic() instead of usleep_ranges() since >>>> IRQ is >>> disabled. >>>> --- >>>> drivers/watchdog/imx7ulp_wdt.c | 29 +++++++++++++++++++++++++++++ >>>> 1 file changed, 29 insertions(+) >>>> >>>> diff --git a/drivers/watchdog/imx7ulp_wdt.c >>>> b/drivers/watchdog/imx7ulp_wdt.c index 7993c8c..7d2b12e 100644 >>>> --- a/drivers/watchdog/imx7ulp_wdt.c >>>> +++ b/drivers/watchdog/imx7ulp_wdt.c >>>> @@ -5,6 +5,7 @@ >>>> >>>> #include >>>> #include >>>> +#include >>>> #include >>>> #include >>>> #include >>>> @@ -36,6 +37,7 @@ >>>> #define DEFAULT_TIMEOUT 60 >>>> #define MAX_TIMEOUT 128 >>>> #define WDOG_CLOCK_RATE 1000 >>>> +#define WDOG_WAIT_TIMEOUT 10000 >>>> >>>> static bool nowayout = WATCHDOG_NOWAYOUT; >>> module_param(nowayout, >>>> bool, 0000); @@ -48,17 +50,31 @@ struct imx7ulp_wdt_device { >>>> struct clk *clk; >>>> }; >>>> >>>> +static inline void imx7ulp_wdt_wait(void __iomem *base, u32 mask) { >>>> + u32 val = readl(base + WDOG_CS); >>>> + >>>> + if (!(val & mask)) >>>> + WARN_ON(readl_poll_timeout_atomic(base + WDOG_CS, val, >>>> + val & mask, 0, >>>> + WDOG_WAIT_TIMEOUT)); >>> >>> I am not a friend of WARN_ON, especially in situations like this. >>> Please explain why this is needed, and why a return of -ETIMEDOUT is >>> not feasible. >> >> OK, I will use return value of -ETIMEOUT and handle it in the caller. > > After a further look, some of the imx7ulp_wdt_wait () callers are void function, so if want > to handle the return value, all those functions return type need to be changed. And, when > the return value is -ETIMEDOUT, the ONLY action is to print out some error message > for these void function, need to use pr_err() due to no dev pointer available, so > do you think it is acceptable to just replace the WARN_ON with pr_err() as below? > First, the point here is that the callers can't do their work if the function times out. So, if the return value isn't necessary, and callers don't need to check it, the function would not be necessary to start with. If it is necessary, and if there is a concern that it can fail, callers should make sure that it actually succeeded. With that in mind, yes, imx7ulp_wdt_init() should fail and return an error, because presumably that is what happened. The same is true for imx7ulp_wdt_enable(). Really, what is the point of detecting a problem just to ignore it ? Second, the wait function is also called _after_ a register was set. In many cases that won't do any good or bad. While it is ok to ignore the error in that case (when nothing else is done), the error message is pointless in that situation. Thanks, Guenter