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Fri, 9 Oct 2026 18:23:25 +0000 From: Ali Rouhi To: "netdev-bot+sashiko@kernel.org" CC: Jiri Pirko , Vadim Fedorenko , Arkadiusz Kubalewski , Ivan Vecera , Jakub Kicinski , Paolo Abeni , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Carolina Jubran , Oleg Zadorozhnyi , "devicetree@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH net-next v11 04/13] dpll: add basic SiTime SiT9531x support Thread-Topic: [PATCH net-next v11 04/13] dpll: add basic SiTime SiT9531x support Thread-Index: AQHdUTShebuE2pn/x0mY8/vS78K0/rbuKg4AgAdqBwA= Date: Fri, 9 Oct 2026 18:23:25 +0000 Message-ID: <20261009182323.76166-2-arouhi@sitime.com> References: <179116259637.434549.13673583471206119318@kernel.org> In-Reply-To: <179116259637.434549.13673583471206119318@kernel.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: mx.microsoft.com 1; dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=sitime.com; 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On Mon, 5 Oct 2026, netdev-bot+sashiko@kernel.org wrote:=0A= =0A= Reply inline.=0A= =0A= > [Severity: Medium]=0A= > Does dropping the cache entry on error keep the cached page selector in= =0A= > sync with the chip? The comment above sit9531x_volatile_reg() says it=0A= > does, but some paths seem to be missed.=0A= =0A= The entry is dropped on every error path the driver controls:=0A= sit9531x_read_u8(), sit9531x_write_u8() and sit9531x_update_pll_u8()=0A= all call sit9531x_page_cache_drop() when regmap returns an error, and=0A= sit9531x_resume() drops it before the first access after a sleep. That=0A= covers the SMBus byte-data case: the failed selector write returns=0A= through one of those three, and the next access re-selects the page.=0A= =0A= > If the failed selector write happens inside a debugfs read, nothing=0A= > drops the entry at all. Can the next sit9531x_write_u8() to page N then= =0A= > land on page P without any error?=0A= =0A= It can, and that window stays. It is not a path the driver takes: the=0A= regmap debugfs registers file is a developer interface that bypasses=0A= every driver on every regmap.=0A= =0A= > A later patch in the series drops the entry on resume. Nothing covers a= =0A= > reset the driver cannot see, though. After one, could writes meant for=0A= > the PLL pages 0x0A-0x0D go to page 0 instead?=0A= =0A= Yes, until the next access that fails or the next resume. Dropping the=0A= entry at the top of each poll tick would bound that window to one poll=0A= period at the cost of one selector write per tick. It is a reasonable=0A= addition and is noted for a later revision rather than folded into this=0A= one.=0A= =0A= > Would it be simpler to make SIT9531X_PAGE_SEL volatile as well?=0A= =0A= SIT9531X_PAGE_SEL is the one register sit9531x_volatile_reg() reports=0A= as non-volatile, so it is the only cached register in the map. Marking=0A= it volatile makes the _regmap_update_bits() in _regmap_select_page()=0A= read the selector from the bus before every access rather than from the=0A= cache, which adds a transfer to each access instead of removing one.=0A= The driver's own paths are already covered, so that cost would buy only=0A= the two windows above.=0A=