On 1/14/20 3:06 AM, Arnaud POULIQUEN wrote: > Hi Bjorn > > On 1/13/20 6:24 PM, Bjorn Andersson wrote: >> On Wed 13 Nov 09:22 PST 2019, Arnaud Pouliquen wrote: >> >>> Return the rpmsg buffer MTU for sending message, so rpmsg users >>> can split a long message in several sub rpmsg buffers. >>> >> >> I won't merge this new api without a client, and I'm still concerned >> about the details. > The client exists: it is the rpmsg tty that i 've been rying to upstream since for a while. > https://patchwork.kernel.org/cover/11130213/ > This patch is the result of some comments you did on rpmsg tty thread. > Suman was also interested in and request to merge it independently > (https://lkml.org/lkml/2019/9/3/774). > That's why i'm trying to do it in 2 steps. > >> >>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@xxxxxx> >>> --- >>> V1 to V2 >>> >>> V1 patch:https://lore.kernel.org/patchwork/patch/1124684/ >>> - Change patch title, >>> - as not solution today to support MTU on GLINK make ops optional, >>> RPMsg client API returns -ENOTSUPP in this case, >>> - suppress smd and glink patches. >> >> That's ok. >> >>> --- >>> drivers/rpmsg/rpmsg_core.c | 21 +++++++++++++++++++++ >>> drivers/rpmsg/rpmsg_internal.h | 2 ++ >>> drivers/rpmsg/virtio_rpmsg_bus.c | 10 ++++++++++ >>> include/linux/rpmsg.h | 10 ++++++++++ >>> 4 files changed, 43 insertions(+) >>> >>> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c >>> index e330ec4dfc33..a6ef54c4779a 100644 >>> --- a/drivers/rpmsg/rpmsg_core.c >>> +++ b/drivers/rpmsg/rpmsg_core.c >>> @@ -283,6 +283,27 @@ int rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src, u32 dst, >>> } >>> EXPORT_SYMBOL(rpmsg_trysend_offchannel); >>> >>> +/** >>> + * rpmsg_get_mtu() - get maximum transmission buffer size for sending message. >>> + * @ept: the rpmsg endpoint >>> + * >>> + * This function returns maximum buffer size available for a single message. >>> + * >>> + * Return: the maximum transmission size on success and an appropriate error >>> + * value on failure. >> >> Is the expectation that a call to rpmsg_send() with this size will >> eventually succeed? > yes, this should be the role of the transport layer > (e.g. RPMsg VirtIO bus) to ensure this. > >> >>> + */ >> [..] >>> +static ssize_t virtio_rpmsg_get_mtu(struct rpmsg_endpoint *ept) >>> +{ >>> + struct rpmsg_device *rpdev = ept->rpdev; >>> + struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev); >>> + >>> + return vch->vrp->buf_size - sizeof(struct rpmsg_hdr); >> >> I'm still under the impression that the rpmsg protocol doesn't have to >> operate on fixed size messages. Would this then return vrp->num_bufs * >> vrp->buf_size / 2 - sizeof(rpmsg_hdr)? There was some discussion in the past to remove the 512 bytes hard-coding and replace it with a configurable value, but that is not yet done. There was some code restructuring towards the same, but it it still fixed atm in virtio_rpmsg transport. > it depends on the transport layer. For RPMsg over virtio, this is the size > of the payload of a buffer so vrp->buf_size - sizeof(rpmsg_hdr) The vrp->num_bufs is the number of buffers available in the vring transport, vrp->buf_size is the size for each transport buffer, and every message includes the rpmsg_hdr structure, so the amount available for rpmsg clients is less by that much. regards Suman
