On wo, 16 okt 2019 23:01:41 +0200, Marc Kleine-Budde wrote: > On 10/16/19 9:06 PM, Elenita Hinds wrote: > > I'm hoping someone can help me with this ... > > > > The DCAN module I'm testing with supports 64 CAN messages and DMA. The > > combined c_can/d_can driver seem to only support 16 RX message objects > > and no DMA (as far as I can tell). > > ACK > > > I noticed that older Linux version > > (3.1) implemented a separate d_can driver that supports both. I'm > > wondering why these were removed from the latest c_can/d_can files. > > Can you give me a pointer to this driver? Are you talking about the > mainline linux-3.1? > > > The reason for this question is I'm seeing frame losses and I think it > > is due to the driver. Increasing the socket buffer sizes did not have > > any effect; the number is overruns was still pretty large. > > > > Any feedback would be appreciated. > > The problem with the c_can and d_can is, that it doesn't have a proper > FIFO but only mailboxes. And these mailboxes don't implement a > timestamp, so that it's not that easy to read messages in the correct order. > > Does the device support bus master DMA? As CAN messages are quite small, > the overhead of setting up DMA might be too high. > > The algorithm that tries to read the CAN frames in the correct order was > added in v3.15. That algorithm should be ported to the rx-offload > helper. This way the mailboxes can be read in interrupt context and not > from NAPI (which runs in softirq context only). > > If this basically works, it can be extended to support 64 mailboxes. I'm facing overflows, and have good results with the patchset I sent last week. As Marc says, reading the mailboxes in NAPI softirq may cause regular overflows. Kurt
