From: Andrew Lunn <email@example.com> To: Asmaa Mnebhi <firstname.lastname@example.org> Cc: Linus Walleij <email@example.com>, Andy Shevchenko <firstname.lastname@example.org>, "open list:GPIO SUBSYSTEM" <email@example.com>, netdev <firstname.lastname@example.org>, linux-kernel <email@example.com>, ACPI Devel Maling List <firstname.lastname@example.org>, Jakub Kicinski <email@example.com>, Bartosz Golaszewski <firstname.lastname@example.org>, "David S. Miller" <email@example.com>, "Rafael J. Wysocki" <firstname.lastname@example.org>, David Thompson <email@example.com> Subject: Re: [PATCH v3 1/2] gpio: mlxbf2: Introduce IRQ support Date: Mon, 27 Sep 2021 16:56:35 +0200 [thread overview] Message-ID: <YVHbo/cJcHzxUkfirstname.lastname@example.org> (raw) In-Reply-To: <CH2PR12MB389585F7D5EFE5E2453593DBD7A79@CH2PR12MB3895.namprd12.prod.outlook.com> On Mon, Sep 27, 2021 at 02:19:45PM +0000, Asmaa Mnebhi wrote: > > > The BlueField GPIO HW only support Edge interrupts. > > O.K. So please remove all level support from this driver, > and return -EINVAL if requested to do level. > This also means, you cannot use interrupts with the > Ethernet PHY. The PHY is using level interrupts. > > Why not? The HW folks said it is alright because they > Do some internal conversion of PHY signal and we have tested > This extensively. So the PHY is level based. The PHY is combing multiple interrupt sources into one external interrupt. If any of those internal interrupt sources are active, the external interrupt is active. If there are multiple active sources at once, the interrupt stays low, until they are all cleared. This means there is not an edge per interrupt. There is one edge when the first internal source occurs, and no more edges, even if there are more internal interrupts. The general flow in the PHY interrupt handler is to read the interrupt status register, which tells you which internal interrupts have fired. You then address these internal interrupts one by one. This can take some time, MDIO is a slow bus etc. While handling these interrupt sources, it could be another internal interrupt source triggers. This new internal interrupt source keeps the external interrupt active. But there has not been an edge, since the interrupt handler is still clearing the sources which caused the first interrupt. With level interrupts, this is not an issue. When the interrupt handler exits, the interrupt is re-enabled. Since it is still active, due to the unhandled internal interrupt sources, the level interrupt immediately fires again. the handler then sees this new interrupt and handles it. At that point the level interrupt goes inactive. Now think about what happens if you are using an edge interrupt controller with a level interrupt. You get the first edge, and call the interrupt handler. And then there are no more edges, despite there being more interrupts. You not only loose the new interrupt, you never see any more interrupts. You PHY link can go up and down, it can try to report being over temperature, that it has detected power from the peer, cable tests have passed, etc. But since there is no edge, there is never an interrupt. So you say it has been extensively tested. Has it been extensively tested with multiple internal interrupt sources at the same time? And with slight timing variations, so that you trigger this race condition? It is not going to happen very often, but when it does, it is going to be very bad. Andrew
next prev parent reply other threads:[~2021-09-27 14:56 UTC|newest] Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-09-23 20:22 [PATCH v3 0/2] gpio: mlxbf2: Introduce proper interrupt handling Asmaa Mnebhi 2021-09-23 20:22 ` [PATCH v3 1/2] gpio: mlxbf2: Introduce IRQ support Asmaa Mnebhi 2021-09-24 11:46 ` Andrew Lunn 2021-09-24 23:48 ` Linus Walleij 2021-09-27 14:04 ` Asmaa Mnebhi 2021-09-27 14:08 ` Andrew Lunn 2021-09-27 14:19 ` Asmaa Mnebhi 2021-09-27 14:26 ` Asmaa Mnebhi 2021-09-27 14:56 ` Andrew Lunn [this message] 2021-09-27 15:52 ` Asmaa Mnebhi 2021-09-27 19:10 ` Andrew Lunn 2021-09-29 19:14 ` Asmaa Mnebhi 2021-09-28 15:02 ` Asmaa Mnebhi 2021-09-29 20:24 ` Andrew Lunn 2021-10-08 14:47 ` Asmaa Mnebhi 2021-09-23 20:22 ` [PATCH v3 2/2] net: mellanox: mlxbf_gige: Replace non-standard interrupt handling Asmaa Mnebhi -- strict thread matches above, loose matches on Subject: below -- 2021-09-23 20:18 [PATCH v3 0/2] gpio: mlxbf2: Introduce proper " Asmaa Mnebhi 2021-09-23 20:18 ` [PATCH v3 1/2] gpio: mlxbf2: Introduce IRQ support Asmaa Mnebhi
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