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Wed, 06 Aug 2025 04:44:09 -0700 (PDT) Message-ID: Date: Wed, 6 Aug 2025 13:44:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] ns16550: ensure polling timer is disarmed To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: dmkhn@proton.me, andrew.cooper3@citrix.com, anthony.perard@vates.tech, julien@xen.org, michal.orzel@amd.com, sstabellini@kernel.org, dmukhin@ford.com, xen-devel@lists.xenproject.org References: <20250730031249.1613142-1-dmukhin@ford.com> <5a4dc92b-139d-4fa5-9baf-2ebc41bba758@suse.com> <78128ec6-b79f-4d4c-a298-72315b190036@suse.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 06.08.2025 12:53, Roger Pau Monné wrote: > On Fri, Aug 01, 2025 at 09:34:42AM +0200, Jan Beulich wrote: >> On 31.07.2025 23:42, dmkhn@proton.me wrote: >>> On Thu, Jul 31, 2025 at 08:54:10AM +0200, Jan Beulich wrote: >>>> On 30.07.2025 20:31, dmkhn@proton.me wrote: >>>>> On Wed, Jul 30, 2025 at 10:12:54AM +0200, Jan Beulich wrote: >>>>>> On 30.07.2025 05:13, dmkhn@proton.me wrote: >>>>>>> From: Denis Mukhin >>>>>>> >>>>>>> As it stands, polling timer is kept in the list of timers even after the >>>>>>> interrupts have been enabled / polling disabled on ns16550-compatible UART. >>>>>>> >>>>>>> Ensure polling timer is removed from the timer list once UART interrupts are >>>>>>> enabled. >>>>>>> >>>>>>> Signed-off-by: Denis Mukhin >>>>>> >>>>>> Wasn't it Andrew(?) who suggested something along these lines? That would >>>>>> want reflecting by a tag then. >>>>> >>>>> Yes, indeed. >>>>> >>>>>> >>>>>> Also, what's the real problem you want to solve here? The timer function >>>>>> would be run one more time after ->intr_works is set, and then the timer >>>>>> will be permanently inactive (up to a possible S3 resume). Is it being on >>>>>> an inactive list an actual problem? (IOW I'd like to understand if the >>>>>> change is merely cosmetic, or if there is some actual benefit.) >>>>> >>>>> My understanding is running polling timer one more time after the interrupts >>>>> are enabled is the issue: if there's a pending timer when it is known the >>>>> timer not needed, then the timer should be canceled. >>>> >>>> And the effort of canceling outweighs the one extra running of the timer? >>> >>> I think so, because intr_works will not flip at run-time once set. >>> If so, no need to keep the timer ready to be rearmed. >> >> Well, to me it looks like a code size increase with extremely limited benefit. >> Hence while likely I wouldn't outright NAK such a change, I also wouldn't ACK >> it. > > Hm, indeed the net win of this is dubious, as the extra polling > interrupt would only happen once. Using stop_timer() would be less > heavyweight than kill_timer(). > > Overall I think it needs justification in the commit message, as the > timer cannot be removed from the list of timers, otherwise it's usage > on resume from suspension will trigger an ASSERT, so part of the > commit message is stale. That could be compensated by another init_timer(), though. (In fact when originally looking at the patch, I [wrongly] thought that path was taken on resume, so didn't comment on that aspect.) Jan