From: Jassi Brar <jassisinghbrar@gmail.com> To: Mikko Perttunen <cyndis@kapsi.fi> Cc: Devicetree List <devicetree@vger.kernel.org>, Greg KH <gregkh@linuxfoundation.org>, mliljeberg@nvidia.com, Mikko Perttunen <mperttunen@nvidia.com>, talho@nvidia.com, Thierry Reding <thierry.reding@gmail.com>, linux-serial@vger.kernel.org, jslaby@suse.com, linux-tegra@vger.kernel.org, ppessi@nvidia.com, Jon Hunter <jonathanh@nvidia.com>, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 01/10] mailbox: Support blocking transfers in atomic context Date: Sat, 8 Dec 2018 11:21:41 +0530 [thread overview] Message-ID: <CABb+yY3_uWv1YVxXxjgygPemBZraCTAXNyXT9G4aTMZv1t7d0g@mail.gmail.com> (raw) In-Reply-To: <4f7a4211-47ee-1114-0974-a3b402178106@kapsi.fi> On Fri, Dec 7, 2018 at 11:50 AM Mikko Perttunen <cyndis@kapsi.fi> wrote: > > On 07/12/2018 11.26, Jassi Brar wrote: > >> I thought that I could also mitigate 2) by busy looping in the TCU driver, > >> but it turns out that that doesn't work. The reason is that since we are > >> in atomic context with all interrupts disabled, the mailbox won't ever > >> consume any new characters, so the read pointer in the circular buffer > >> won't increment, leaving me with no condition upon which to loop that > >> would work. > >> > > So you want to be able to rely on an emulated console (running on a > > totally different subsystem) to dump development-phase early-boot > > logs? At the cost of legitimizing busy looping in atomic context - one > > random driver messing up the api for ever. Maybe you could have the > > ring buffer in some shmem and only pass the number of valid characters > > in it, to the remote? > > > > I would like to note that this is the one and only console interface > that exists on these systems, for both development phase and production. > Other UARTs are not externally accessible on the systems, or they are > comparatively difficult to access as they aren't intended to be used as > consoles in the system design. > The combination of hardware and firmware > implementing the console is black box from software's point of view > (similarly to any other UART HW). The interface has also been fixed at > an early system design phase, as there are many operating systems > running on these boards, each with their own drivers. > That is the saddest part - someone, who writes test cases for the h/w team and with almost no knowledge of how OSes work, decides how the firmware is going to work and calls it done. Then the Linux is left to deal with the mess as we "can't do anything about it".
WARNING: multiple messages have this Message-ID (diff)
From: Jassi Brar <jassisinghbrar@gmail.com> To: Mikko Perttunen <cyndis@kapsi.fi> Cc: Devicetree List <devicetree@vger.kernel.org>, Greg KH <gregkh@linuxfoundation.org>, mliljeberg@nvidia.com, Mikko Perttunen <mperttunen@nvidia.com>, talho@nvidia.com, Thierry Reding <thierry.reding@gmail.com>, linux-serial@vger.kernel.org, jslaby@suse.com, linux-tegra@vger.kernel.org, ppessi@nvidia.com, Jon Hunter <jonathanh@nvidia.com>, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 01/10] mailbox: Support blocking transfers in atomic context Date: Sat, 8 Dec 2018 11:21:41 +0530 [thread overview] Message-ID: <CABb+yY3_uWv1YVxXxjgygPemBZraCTAXNyXT9G4aTMZv1t7d0g@mail.gmail.com> (raw) In-Reply-To: <4f7a4211-47ee-1114-0974-a3b402178106@kapsi.fi> On Fri, Dec 7, 2018 at 11:50 AM Mikko Perttunen <cyndis@kapsi.fi> wrote: > > On 07/12/2018 11.26, Jassi Brar wrote: > >> I thought that I could also mitigate 2) by busy looping in the TCU driver, > >> but it turns out that that doesn't work. The reason is that since we are > >> in atomic context with all interrupts disabled, the mailbox won't ever > >> consume any new characters, so the read pointer in the circular buffer > >> won't increment, leaving me with no condition upon which to loop that > >> would work. > >> > > So you want to be able to rely on an emulated console (running on a > > totally different subsystem) to dump development-phase early-boot > > logs? At the cost of legitimizing busy looping in atomic context - one > > random driver messing up the api for ever. Maybe you could have the > > ring buffer in some shmem and only pass the number of valid characters > > in it, to the remote? > > > > I would like to note that this is the one and only console interface > that exists on these systems, for both development phase and production. > Other UARTs are not externally accessible on the systems, or they are > comparatively difficult to access as they aren't intended to be used as > consoles in the system design. > The combination of hardware and firmware > implementing the console is black box from software's point of view > (similarly to any other UART HW). The interface has also been fixed at > an early system design phase, as there are many operating systems > running on these boards, each with their own drivers. > That is the saddest part - someone, who writes test cases for the h/w team and with almost no knowledge of how OSes work, decides how the firmware is going to work and calls it done. Then the Linux is left to deal with the mess as we "can't do anything about it". _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2018-12-08 5:51 UTC|newest] Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-11-12 15:18 [PATCH v2 00/10] serial: Add Tegra Combined UART driver Thierry Reding 2018-11-12 15:18 ` Thierry Reding 2018-11-12 15:18 ` [PATCH v2 01/10] mailbox: Support blocking transfers in atomic context Thierry Reding 2018-11-12 15:18 ` Thierry Reding 2018-11-17 17:27 ` Jassi Brar 2018-11-17 17:27 ` Jassi Brar 2018-11-20 15:29 ` Thierry Reding 2018-11-20 15:29 ` Thierry Reding 2018-11-21 14:27 ` Thierry Reding 2018-11-21 14:27 ` Thierry Reding 2018-11-22 2:18 ` Jassi Brar 2018-11-22 2:18 ` Jassi Brar 2018-11-22 8:47 ` Thierry Reding 2018-11-22 8:47 ` Thierry Reding 2018-11-22 16:07 ` Jassi Brar 2018-11-22 16:07 ` Jassi Brar 2018-11-22 17:34 ` Thierry Reding 2018-11-22 17:34 ` Thierry Reding 2018-11-23 11:17 ` Thierry Reding 2018-11-23 11:17 ` Thierry Reding 2018-11-23 11:56 ` Thierry Reding 2018-11-23 11:56 ` Thierry Reding 2018-11-28 9:43 ` Jon Hunter 2018-11-28 9:43 ` Jon Hunter 2018-11-28 10:08 ` Thierry Reding 2018-11-28 10:08 ` Thierry Reding 2018-11-29 5:23 ` Jassi Brar 2018-11-29 5:23 ` Jassi Brar 2018-11-29 15:23 ` Thierry Reding 2018-12-07 5:56 ` Jassi Brar 2018-12-07 5:56 ` Jassi Brar 2018-12-07 6:19 ` Mikko Perttunen 2018-12-07 6:19 ` Mikko Perttunen 2018-12-08 5:51 ` Jassi Brar [this message] 2018-12-08 5:51 ` Jassi Brar 2018-12-08 8:50 ` Greg KH 2018-12-08 8:50 ` Greg KH 2018-12-09 1:20 ` Jassi Brar 2018-12-09 1:20 ` Jassi Brar 2018-12-07 11:32 ` Thierry Reding 2018-12-07 15:39 ` Greg KH 2018-12-07 15:39 ` Greg KH 2018-12-08 6:09 ` Jassi Brar 2018-12-08 6:09 ` Jassi Brar 2018-12-10 9:52 ` Thierry Reding 2018-12-10 20:30 ` Jassi Brar 2018-12-10 20:30 ` Jassi Brar 2018-12-10 20:45 ` Thierry Reding 2018-12-10 21:32 ` Jassi Brar 2018-12-10 21:32 ` Jassi Brar 2018-11-12 15:18 ` [PATCH v2 02/10] mailbox: Allow multiple controllers per device Thierry Reding 2018-11-12 15:18 ` Thierry Reding 2018-11-12 15:18 ` [PATCH v2 03/10] dt-bindings: tegra186-hsp: Add shared mailboxes Thierry Reding 2018-11-12 15:18 ` Thierry Reding 2018-11-12 15:18 ` [PATCH v2 04/10] mailbox: tegra-hsp: Add support for " Thierry Reding 2018-11-12 15:18 ` Thierry Reding 2018-11-13 11:09 ` Jon Hunter 2018-11-13 11:09 ` Jon Hunter 2018-11-13 13:09 ` Thierry Reding 2018-11-13 13:09 ` Thierry Reding 2018-11-13 19:24 ` Jon Hunter 2018-11-13 19:24 ` Jon Hunter 2018-11-12 15:18 ` [PATCH v2 05/10] mailbox: tegra-hsp: Add suspend/resume support Thierry Reding 2018-11-12 15:18 ` Thierry Reding 2018-11-13 11:17 ` Jon Hunter 2018-11-13 11:17 ` Jon Hunter 2018-12-10 9:58 ` Thierry Reding 2018-11-12 15:18 ` [PATCH v2 06/10] dt-bindings: serial: Add bindings for nvidia, tegra194-tcu Thierry Reding 2018-11-12 15:18 ` Thierry Reding 2018-11-13 9:39 ` [PATCH v2 06/10] dt-bindings: serial: Add bindings for nvidia,tegra194-tcu Jon Hunter 2018-11-13 9:39 ` Jon Hunter 2018-11-13 10:03 ` Thierry Reding 2018-11-13 10:03 ` Thierry Reding 2018-11-13 10:11 ` Jon Hunter 2018-11-13 10:11 ` Jon Hunter 2018-11-12 15:18 ` [PATCH v2 07/10] serial: Add Tegra Combined UART driver Thierry Reding 2018-11-12 15:18 ` Thierry Reding 2018-11-12 15:18 ` [PATCH v2 08/10] arm64: tegra: Add nodes for TCU on Tegra194 Thierry Reding 2018-11-12 15:18 ` Thierry Reding 2018-11-12 15:18 ` [PATCH v2 09/10] arm64: tegra: Mark TCU as primary serial port on Tegra194 P2888 Thierry Reding 2018-11-12 15:18 ` Thierry Reding 2018-11-12 15:18 ` [PATCH v2 10/10] arm64: defconfig: Enable Tegra TCU Thierry Reding 2018-11-12 15:18 ` Thierry Reding
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