Hi Finn, Geert, >>>>> + /* We are passed DMA addresses i.e. physical addresses, but must >>>>> use >>>>> + * kernel virtual addresses here, so remap to virtual. This is >>>>> easy >>>>> + * enough for the case of residual bytes of an extended message in >>>>> + * transfer - we know the address must be esp->command_block_dma. >>>>> + * In other cases, hope that phys_to_virt() works ... >>>>> + */ >>>>> + if (addr == esp->command_block_dma) >>>>> + addr = (u32) esp->command_block; >>>>> + else >>>>> + addr = (u32) phys_to_virt(addr); >>>> >>>> To avoid having a need for phys_to_virt(), you should remember the >>>> addresses passed to/returned from dma_map_*(). >>> >>> Interesting - can we be certain that only one mapping is being used at >>> any one time?
Tests have revealed that we can't rely on a single mapping active at any one time (it's rare, but I get some messages printed when I log zorro_esp_map_single() being called with a mapping already saved). >>> >> >> I don't know how Geert's suggestion would work in this case. But I think > > I suppose storing the virtual address in the driver private data struct, > and looking up that stored virtual address in the PIO transfer function. > >> we covered this problem back in December: >> https://marc.info/?l=linux-m68k&m=151365452606870 >> >> (That thread also helps explain the PIO vs. ESP_CMD_SELAS issue.) > > Yes, rereading that thread now suggests we had explored a few options > but the issue of autosense commands was making it a little too complicated. We have no need to find out the correct virtual address for a given DMA mapping as long as we only use PIO for message byte transfer. I'll leave finding a proper solution for a rainy day (or rather, a few rainy weeks). Anyone familiar with Auckland will know what that means :-) Cheers, Michael
