On 4/9/19 12:14 PM, xiang xiao wrote: > On Tue, Apr 9, 2019 at 3:28 PM Arnaud Pouliquen <arnaud.pouliquen@xxxxxx> wrote: >> >> >> >> On 4/8/19 3:29 PM, xiang xiao wrote: >>> On Mon, Apr 8, 2019 at 8:05 PM Arnaud Pouliquen <arnaud.pouliquen@xxxxxx> wrote: >>>> >>>> >>>> >>>> On 4/6/19 9:56 AM, xiang xiao wrote: >>>>> On Sat, Apr 6, 2019 at 12:08 AM Arnaud Pouliquen >>>>> <arnaud.pouliquen@xxxxxx> wrote: >>>>>> >>>>>> >>>>>> >>>>>> On 4/5/19 4:03 PM, xiang xiao wrote: >>>>>>> On Fri, Apr 5, 2019 at 8:33 PM Arnaud Pouliquen <arnaud.pouliquen@xxxxxx> wrote: >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> On 4/5/19 12:12 PM, xiang xiao wrote: >>>>>>>>> On Fri, Apr 5, 2019 at 12:14 AM Arnaud Pouliquen >>>>>>>>> <arnaud.pouliquen@xxxxxx> wrote: >>>>>>>>>> >>>>>>>>>> Hello Xiang, >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> On 4/3/19 2:47 PM, xiang xiao wrote: >>>>>>>>>>> On Thu, Mar 21, 2019 at 11:48 PM Fabien Dessenne <fabien.dessenne@xxxxxx> wrote: >>>>>>>>>>>> >>>>>>>>>>>> This driver exposes a standard tty interface on top of the rpmsg >>>>>>>>>>>> framework through the "rpmsg-tty-channel" rpmsg service. >>>>>>>>>>>> >>>>>>>>>>>> This driver supports multi-instances, offering a /dev/ttyRPMSGx entry >>>>>>>>>>>> per rpmsg endpoint. >>>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> How to support multi-instances from the same remoteproc instance? I >>>>>>>>>>> saw that the channel name is fixed to "rpmsg-tty-channel" which mean >>>>>>>>>>> only one channel can be created for each remote side. >>>>>>>>>> The driver is multi-instance based on muti-endpoints on top of the >>>>>>>>>> "rpmsg-tty-channel" service. >>>>>>>>>> On remote side you just have to call rpmsg_create_ept with destination >>>>>>>>>> address set to ANY. The result is a NS service announcement that trigs a >>>>>>>>>> probe with a new endpoint. >>>>>>>>>> You can find code example for the remote side here: >>>>>>>>>> https://github.com/STMicroelectronics/STM32CubeMP1/blob/master/Projects/STM32MP157C-DK2/Applications/OpenAMP/OpenAMP_TTY_echo/Src/main.c >>>>>>>>> >>>>>>>>> Demo code create two uarts(huart0 and huart1), and both use the same >>>>>>>>> channel name( "rpmsg-tty-channel"). >>>>>>>>> But rpmsg_create_channel in kernel will complain the duplication: >>>>>>>>> /* make sure a similar channel doesn't already exist */ >>>>>>>>> tmp = rpmsg_find_device(dev, chinfo); >>>>>>>>> if (tmp) { >>>>>>>>> /* decrement the matched device's refcount back */ >>>>>>>>> put_device(tmp); >>>>>>>>> dev_err(dev, "channel %s:%x:%x already exist\n", >>>>>>>>> chinfo->name, chinfo->src, chinfo->dst); >>>>>>>>> return NULL; >>>>>>>>> } >>>>>>>>> Do you have some local change not upstream yet? >>>>>>>> Nothing is missing. There is no complain as the function >>>>>>>> rpmsg_device_match returns 0, because the chinfo->dst (that corresponds >>>>>>>> to the remote ept address) is different. >>>>>>>> >>>>>>> >>>>>>> Yes, you are right. >>>>>>> >>>>>>>> If i well remember you have also a similar implementation of the service >>>>>>>> on your side. Do you see any incompatibility with your implementation? >>>>>>>> >>>>>>> >>>>>>> Our implementation is similar to yours, but has two major difference: >>>>>>> 1.Each instance has a different channel name but share the same prefix >>>>>>> "rpmsg-tty*", the benefit is that: >>>>>>> a.Device name(/dev/tty*) is derived from rpmsg-tty*, instead the >>>>>>> random /dev/ttyRPMSGx >>>>>>> b.Don't need tty_idr to allocate the unique device id >>>>>> I understand the need but in your implementation it look like you hack >>>>>> the rpmsg service to instantiate your tty... you introduce a kind of >>>>>> meta rpmsg tty service with sub-service related to the serial content. >>>>>> Not sure that this could be upstreamed... >>>>> >>>>> Not too much hack here, the only change in common is: >>>>> 1.Add match callback into rpmsg_driver >>>>> 2.Call match callback in rpmsg_dev_match >>>>> so rpmsg driver could join the bus match decision process(e.g. change >>>>> the exact match to the prefix match). >>>>> The similar mechanism exist in other subsystem for many years. >>>> The mechanism also exists in rpmsg but based on the service. it is >>>> similar to the compatible, based on the rpmsg_device_id structure that >>>> should list the cervices supported. >>> >>> But match callback is much flexible than rpmsg_device_id table, the >>> table is fixed at compile time, match callback could do all matic at >>> the runtime. >> Today this not the way rpmsg implements the service but declares it on >> registration. This is an evolution of the rpmsg, so better to propose it >> in a separate thread. >> > > Here is the patch I post before: > https://patchwork.kernel.org/patch/10791741/ > >>> >>>> My concern here is that you would like to expose the service on top of >>>> the tty while aim of this driver is just to expose a tty over rpmsg. So >>>> in this case seems not a generic implementation but a platform dependent >>>> implementation. >>>> >>> >>> I can't understand why the implementation is platform dependent, could >>> you explain more details?In your uart_rpmsg/c. >> the rpmsg service is "rpmsg-tty" this is a "standard" service. But you >> define a "rpmsg-ttyxxxx" service because you want to expose a service on >> top of the tty service, not the tty service itself. In this way you are >> not able to list this service in rpmsg_device_id because not standard >> static service, you have to implement the match. This look like you >> adapt rpmsg protocol to match with your platform implementation. >> >>> >>>>> >>>>>> proposal to integrate your need in the ST driver: it seems possible to >>>>>> have /dev/ttyRPMSGx with x corresponding to the remote endpoint address? >>>>>> So if you want to have a fixed tty name you can fix the remote endpoint. >>>>>> Is it something reasonable for you? >>>>> >>>>> But in our system, we have more than ten rpmsg services running at the >>>>> same time, it's difficult to manage them by the hardcode endpoint >>>>> address. >>>> Seems not so difficult. Today you identify your service by a name. Seems >>>> just a matter of changing it by an address, it just an identifier by an >>>> address instead of a string. >>> >>> But I still prefer to use string(channel name) not number(port) to >>> manage the multiple rpmsg instance: >>> 1.Just like nobody prefer use ip address not domain name. >> when i have a look in /dev/tty, a number is generaly used to instantiate >> the same device type. For instance if you have several tty over USB, you >> have several instantiation of the ttyACM, nothing linked to the service >> on top of the link. >> Here from my point of view it is the same. >> >>> 2.rpmsg protocol support name and port mapping natively, why not use it? >> Precisely we want to use native implementation of the protocol, not to >> extend it with the match function that introduces a meta service notion. >> >> I'm not sure that we can find a compromise on this point. So I would >> like to propose you to do this in 2 steps: >> step 1: we start on basic RPMsg service, (with ept addr as port ID, if >> you are interesting in). >> step 2: you send patch on top to propose rpmsg match function, with tty >> naming based on feature name (with support of the legacy). >> > > It is fine to put the naming tty to another patch. For the first step: I tested the use of ept dest address as index, not possible as it is used by core part as table index. I have to keep basic indexation. So this will give you argument for your add-on patch. > >>>>> >>>>>> >>>>>> >>>>>>> 2.Each transfer need get response from peer to avoid the buffer >>>>>>> overflow. This is very important if the peer use pull >>>>>>> model(read/write) instead of push model(callback). >>>>>> I not sure to understand your point... You mean that you assume that the >>>>>> driver should be blocked until a response from the remote side? >>>>> >>>>> For example, in your RTOS demo code: >>>>> 1.VIRT_UART0_RxCpltCallback save the received data in a global buffer >>>>> VirtUart0ChannelBuffRx >>>>> 2.Main loop poll VirtUart0RxMsg flag and echo the data back to kernel >>>>> if this flag is set >>>>> Between step1 and step 2, kernel may send additional data and then >>>>> overwrite the data not get processed by main loop. >>>>> It's very easy to reproduce by: >>>>> cat /dev/ttyRPMSGx > /tmp/dump & >>>>> cat /a/huge/file > /dev/ttyRPMSGx >>>>> diff /a/hug/file /tmp/dump >>>> Yes our example is very limited, aim is not to be robust for this use >>>> case but just giving a simple sample to allow user to send a simple text >>>> in console and echo it. >>>>> The push model mean the receiver could process the data completely in >>>>> callback context, and >>>>> the pull model mean the receiver just save the data in buffer and >>>>> process it late(e.g. by read call). >>>> Thanks for the clarification. >>>>>> This seems not compatible with a "generic" tty and with Johan remarks: >>>>>> "Just a drive-by comment; it looks like rpmsg_send() may block, but >>>>>> the tty-driver write() callback must never sleep." >>>>>> >>>>> >>>>> The handshake doesn't mean the write callback must block, we can >>>>> provide write_room callback to tell tty core to stop sending. >>>> In the write function you have implemented the wait_for_completion that >>>> blocks, waiting answer from the remote side. For instance in case of >>>> remote firmware crash, you should be blocked. >>> >>> This just make the code simple, and can be fixed by the classic slide >>> window algo easily. >> But i still not understand while we should wait an answer on a message. > > With the slide window algo: > 1.Exchange the buffer size at the beginning > 2.Any side send data and decrease the buffer size > 3.Implement write_room callback to return the left buffer size > 4.tty framework stop to call write callack if write_room return 0 > Since rpmsg transport is reliable, the receiver don't need send > acknowledge and then the sender don't need wait the response. > But the receiver need to send the message to report the new slide > window size after anybody read some data from buffer. Seems very complex for a tty purpose. If room is set to RPMSG buffer size the bottle-neck is the RPMsg buffers availability. This should be detected by returning 0 on write if no buffer available, using rpmsg_trysend. Now i can see 2 use-cases that could need flow control. 1) receiver want to stop the transfer in reception: => similar to RTS/CTS 2) need flow control on RPMsg to share the buffer between different services (not only tty). => In this second case this should be manage in RPMsg. This need has already been identified during discussion in community. Could be managed based on a max bandwith request ( size or number of RPMsg buffer) controlled by the RPMsg core... > >> The ack should be client dependent, not part of the protocol. >> Furthemore a issue of this is that the line discipline allows to echo >> every chars received on tty dev. This would generate an infinite loop as >> the remote also echo it. > > For the loopback test, we should disable line discipline echo.
