From: Jassi Brar <jassisinghbrar@gmail.com> To: Bjorn Andersson <bjorn.andersson@linaro.org> Cc: Jeffrey Hugo <jhugo@codeaurora.org>, Andy Gross <andy.gross@linaro.org>, Rob Herring <robh+dt@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Ohad Ben-Cohen <ohad@wizery.com>, linux-arm-msm@vger.kernel.org, linux-soc@vger.kernel.org, Devicetree List <devicetree@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-remoteproc@vger.kernel.org Subject: Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Date: Tue, 9 May 2017 22:11:22 +0530 [thread overview] Message-ID: <CABb+yY2uC6vNFTq1KtZwrrw8x4BEfc2cMjF5DwrLbGpYWBNBzQ@mail.gmail.com> (raw) In-Reply-To: <20170508191154.GM15143@minitux> On Tue, May 9, 2017 at 12:41 AM, Bjorn Andersson <bjorn.andersson@linaro.org> wrote: > On Sun 07 May 23:47 PDT 2017, Jassi Brar wrote: > >> On Mon, May 8, 2017 at 11:24 AM, Bjorn Andersson >> <bjorn.andersson@linaro.org> wrote: >> > On Fri 05 May 21:48 PDT 2017, Jassi Brar wrote: >> > >> > The APCS IPC register serves the basis for all inter-processor >> > communication in a Qualcomm platform, so it's not only the RPM driver >> > discussed earlier that uses this. It's also used for other non-FIFO >> > based communication channels, where the signalled information either >> > isn't acked at all or acked on a system-level. >> > >> Something has to indicate consumption of data or "requested action >> taken". Otherwise the protocol is design-wise broken. >> > > The SMD and GLINK protocols work by providing two independent one-way > pipes that higher levels can use to send and receive messages. When some > driver pushes a message into the transmit-pipe we check if there's > space, then write the message, signal the remote (APCS IPC) and then > return. > "we check if there's space" -> this is what mailbox api tries to do with last_tx_done before starting the next message. >> >> The client should call mbox_client_txdone() after >> >> mbox_send_message(). >> > >> > So every time we call mbox_send_message() from any of the client drivers >> > we also needs to call mbox_client_txdone()? >> > >> Yes. >> >> > This seems like an awkward side effect of using the mailbox framework - >> > which has to be spread out in at least 6 different client drivers :( >> > >> No. Mailbox or whatever you implement - you must (and do) tick the >> state machine to keep the messages moving. > > But the state you have in the other mailbox drivers is not a concern of > the APCS IPC. > No, as you say above you check for space before writing the next message, this is what I call ticking the state machine. >> Best designs have some interrupt occurring when the message has been >> consumed by the remote. Some designs have a flag set which needs to be >> polled to detect completion. Very few (like yours) that support >> neither irq nor polling, have to be driven by the upper protocol layer >> by some ack packet (or tracking read/write pointers like you do). >> These three cases are denoted by TXDONE_BY_IRQ, TXDONE_BY_POLL and >> TXDONE_BY_ACK respectively. >> > > You're confusing the APCS IPC with the larger communication mechanism, > Maybe. I am not versed with QCom technologies like RPM, SMD, GLINK, APCS etc. Controller driver is what physically transmits a signal to remote. Users above the mailbox api are client drivers. > > This is why I suggested that this is a doorbell, rather than a mailbox. > Your argumentation of how a mailbox should work makes perfect sense, but > it's not how the Qualcomm IPC works. > Mailbox framework is designed to support, what you call doorbell type of communication, just fine. There is no need to define another class. > > Setting TXDONE_BY_POLL and specifying a dummy last_tx_done() comes with > a crazy overhead. To set a single bit in a register we will take the > channel spinlock 4 times, start a timer, iterate over all registered > channels and the client must be marked as blocking so we will get at > least 2 additional context switches. > How often does the platform send messages for it to be a considerable load? BTW, this is an option only if your client driver doesn't want to explicitly tick the state machine by calling mbox_client_txdone()... which I think should be done in the first place. thanks
WARNING: multiple messages have this Message-ID (diff)
From: Jassi Brar <jassisinghbrar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> To: Bjorn Andersson <bjorn.andersson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> Cc: Jeffrey Hugo <jhugo-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>, Andy Gross <andy.gross-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>, Ohad Ben-Cohen <ohad-Ix1uc/W3ht7QT0dZR+AlfA@public.gmane.org>, linux-arm-msm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Devicetree List <devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linux Kernel Mailing List <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, linux-remoteproc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Subject: Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Date: Tue, 9 May 2017 22:11:22 +0530 [thread overview] Message-ID: <CABb+yY2uC6vNFTq1KtZwrrw8x4BEfc2cMjF5DwrLbGpYWBNBzQ@mail.gmail.com> (raw) In-Reply-To: <20170508191154.GM15143@minitux> On Tue, May 9, 2017 at 12:41 AM, Bjorn Andersson <bjorn.andersson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote: > On Sun 07 May 23:47 PDT 2017, Jassi Brar wrote: > >> On Mon, May 8, 2017 at 11:24 AM, Bjorn Andersson >> <bjorn.andersson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote: >> > On Fri 05 May 21:48 PDT 2017, Jassi Brar wrote: >> > >> > The APCS IPC register serves the basis for all inter-processor >> > communication in a Qualcomm platform, so it's not only the RPM driver >> > discussed earlier that uses this. It's also used for other non-FIFO >> > based communication channels, where the signalled information either >> > isn't acked at all or acked on a system-level. >> > >> Something has to indicate consumption of data or "requested action >> taken". Otherwise the protocol is design-wise broken. >> > > The SMD and GLINK protocols work by providing two independent one-way > pipes that higher levels can use to send and receive messages. When some > driver pushes a message into the transmit-pipe we check if there's > space, then write the message, signal the remote (APCS IPC) and then > return. > "we check if there's space" -> this is what mailbox api tries to do with last_tx_done before starting the next message. >> >> The client should call mbox_client_txdone() after >> >> mbox_send_message(). >> > >> > So every time we call mbox_send_message() from any of the client drivers >> > we also needs to call mbox_client_txdone()? >> > >> Yes. >> >> > This seems like an awkward side effect of using the mailbox framework - >> > which has to be spread out in at least 6 different client drivers :( >> > >> No. Mailbox or whatever you implement - you must (and do) tick the >> state machine to keep the messages moving. > > But the state you have in the other mailbox drivers is not a concern of > the APCS IPC. > No, as you say above you check for space before writing the next message, this is what I call ticking the state machine. >> Best designs have some interrupt occurring when the message has been >> consumed by the remote. Some designs have a flag set which needs to be >> polled to detect completion. Very few (like yours) that support >> neither irq nor polling, have to be driven by the upper protocol layer >> by some ack packet (or tracking read/write pointers like you do). >> These three cases are denoted by TXDONE_BY_IRQ, TXDONE_BY_POLL and >> TXDONE_BY_ACK respectively. >> > > You're confusing the APCS IPC with the larger communication mechanism, > Maybe. I am not versed with QCom technologies like RPM, SMD, GLINK, APCS etc. Controller driver is what physically transmits a signal to remote. Users above the mailbox api are client drivers. > > This is why I suggested that this is a doorbell, rather than a mailbox. > Your argumentation of how a mailbox should work makes perfect sense, but > it's not how the Qualcomm IPC works. > Mailbox framework is designed to support, what you call doorbell type of communication, just fine. There is no need to define another class. > > Setting TXDONE_BY_POLL and specifying a dummy last_tx_done() comes with > a crazy overhead. To set a single bit in a register we will take the > channel spinlock 4 times, start a timer, iterate over all registered > channels and the client must be marked as blocking so we will get at > least 2 additional context switches. > How often does the platform send messages for it to be a considerable load? BTW, this is an option only if your client driver doesn't want to explicitly tick the state machine by calling mbox_client_txdone()... which I think should be done in the first place. thanks -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html
next prev parent reply other threads:[~2017-05-09 16:41 UTC|newest] Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-05-04 20:05 [PATCH v4 1/5] mailbox: Make startup and shutdown ops optional Bjorn Andersson 2017-05-04 20:05 ` [PATCH v4 2/5] dt-bindings: mailbox: Introduce Qualcomm APCS global binding Bjorn Andersson 2017-05-04 20:05 ` [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Bjorn Andersson 2017-05-05 10:26 ` Jassi Brar 2017-05-05 18:37 ` Bjorn Andersson 2017-05-05 19:22 ` Jassi Brar 2017-05-05 19:22 ` Jassi Brar 2017-05-05 19:53 ` Jeffrey Hugo 2017-05-05 19:53 ` Jeffrey Hugo [not found] ` <CABb+yY3fcFkVfJX0CuBenDLek7ew80HFAKLxtthrhBLWJZv5Kw@mail.gmail.com> [not found] ` <CABb+yY2jHER98Mtfigg9rwA5PGsZt2UMm=5SWhrqvsqF-Yai=Q@mail.gmail.com> [not found] ` <CABb+yY3XW3HmJop0cJ2NZzqCtkWtvKgco9ecUt8890DKpZeaag@mail.gmail.com> [not found] ` <CABb+yY0beZmy8qSsxLoikKeXnijmded4oGRrckW+jZEqKV9jPw@mail.gmail.com> 2017-05-05 20:11 ` Jassi Brar 2017-05-05 20:22 ` Jassi Brar 2017-05-05 20:39 ` Jeffrey Hugo 2017-05-06 1:19 ` Bjorn Andersson 2017-05-06 1:19 ` Bjorn Andersson 2017-05-06 4:48 ` Jassi Brar 2017-05-08 5:54 ` Bjorn Andersson 2017-05-08 6:47 ` Jassi Brar 2017-05-08 6:47 ` Jassi Brar 2017-05-08 19:11 ` Bjorn Andersson 2017-05-09 16:41 ` Jassi Brar [this message] 2017-05-09 16:41 ` Jassi Brar 2017-05-09 19:11 ` Bjorn Andersson 2017-05-09 19:11 ` Bjorn Andersson 2017-05-10 2:33 ` Jassi Brar 2017-05-10 2:33 ` Jassi Brar 2017-05-10 19:00 ` Bjorn Andersson 2017-05-11 2:07 ` Jassi Brar 2017-05-11 2:07 ` Jassi Brar 2017-05-12 22:48 ` Bjorn Andersson 2017-05-16 11:25 ` Jassi Brar 2017-05-16 11:25 ` Jassi Brar 2017-05-04 20:05 ` [PATCH v4 4/5] soc: qcom: Add device tree binding for GLINK RPM Bjorn Andersson 2017-05-08 17:06 ` Rob Herring 2017-05-08 17:53 ` Bjorn Andersson 2017-05-04 20:05 ` [PATCH v4 5/5] rpmsg: Introduce Qualcomm RPM glink driver Bjorn Andersson 2017-05-05 9:35 ` [PATCH v4 1/5] mailbox: Make startup and shutdown ops optional Sudeep Holla 2017-05-05 9:35 ` Sudeep Holla 2017-05-05 9:35 ` Sudeep Holla 2017-05-05 10:33 ` Jassi Brar 2017-05-05 10:33 ` Jassi Brar 2017-05-05 18:21 ` Bjorn Andersson
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