On 10.05.2021 14:25:15, Marc Kleine-Budde wrote: > On 09.05.2021 14:43:09, Dario Binacchi wrote: > > As reported by a comment in the c_can_start_xmit() this was not a FIFO. > > C/D_CAN controller sends out the buffers prioritized so that the lowest > > buffer number wins. > > > > What did c_can_start_xmit() do if it found tx_active = 0x80000000 ? It > > waited until the only frame of the FIFO was actually transmitted by the > > controller. Only one message in the FIFO but we had to wait for it to > > empty completely to ensure that the messages were transmitted in the > > order in which they were loaded. > > > > By storing the frames in the FIFO without requiring its transmission, we > > will be able to use the full size of the FIFO even in cases such as the > > one described above. The transmission interrupt will trigger their > > transmission only when all the messages previously loaded but stored in > > less priority positions of the buffers have been transmitted. > > The algorithm you implemented looks a bit too complicated to me. Let me > sketch the algorithm that's implemented by several other drivers. > > - have a power of two number of TX objects > - add a number of objects to struct priv (tx_num) > (or make it a define, if the number of tx objects is compile time fixed) > - add two "unsigned int" variables to your struct priv, > one "tx_head", one "tx_tail" > - the hard_start_xmit() writes to priv->tx_head & (priv->tx_num - 1) > - increment tx_head > - stop the tx_queue if there is no space or if the object with the > lowest prio has been written > - in TX complete IRQ, handle priv->tx_tail object > - increment tx_tail > - wake queue if there is space but don't wake if we wait for the lowest > prio object to be TX completed. > > Special care needs to be taken to implement that lock-less and race > free. I suggest to look the the mcp251xfd driver. After converting the driver to the above outlined implementation it should be more straight forward to add the caching you implemented. regards, Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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