On 13/04/16 14:49, Vinod Koul wrote: > On Tue, Apr 12, 2016 at 05:23:32PM +0100, Jon Hunter wrote: >>>>> why should this be hard coded in kernel and not queried from something like >>>>> DT? This case seems to be hardware property >>>> >>>> Originally, I did have this in DT, however, the Tegra maintainers prefer >>>> this and this is consistent with the other Tegra DMA driver (see >>>> driver/dma/tegra20-apb-dma.c) [0]. >>> >>> But this creates a problem when you have next generation of controller with >>> different channel count! >>> How do we solve then? >> >> Same way we solve this for the tegra20-apb-dma driver by having >> different chip data per SoC in the driver ... >> >> 1259 /* Tegra20 specific DMA controller information */ >> 1260 static const struct tegra_dma_chip_data tegra20_dma_chip_data = { >> 1261 .nr_channels = 16, >> 1262 .channel_reg_size = 0x20, >> 1263 .max_dma_count = 1024UL * 64, >> 1264 .support_channel_pause = false, >> 1265 .support_separate_wcount_reg = false, >> 1266 }; >> 1267 >> 1268 /* Tegra30 specific DMA controller information */ >> 1269 static const struct tegra_dma_chip_data tegra30_dma_chip_data = { >> 1270 .nr_channels = 32, >> 1271 .channel_reg_size = 0x20, >> 1272 .max_dma_count = 1024UL * 64, >> 1273 .support_channel_pause = false, >> 1274 .support_separate_wcount_reg = false, >> 1275 }; >> 1276 >> 1277 /* Tegra114 specific DMA controller information */ >> 1278 static const struct tegra_dma_chip_data tegra114_dma_chip_data = { >> 1279 .nr_channels = 32, >> 1280 .channel_reg_size = 0x20, >> 1281 .max_dma_count = 1024UL * 64, >> 1282 .support_channel_pause = true, >> 1283 .support_separate_wcount_reg = false, >> 1284 }; >> 1285 >> 1286 /* Tegra148 specific DMA controller information */ >> 1287 static const struct tegra_dma_chip_data tegra148_dma_chip_data = { >> 1288 .nr_channels = 32, >> 1289 .channel_reg_size = 0x40, >> 1290 .max_dma_count = 1024UL * 64, >> 1291 .support_channel_pause = true, >> 1292 .support_separate_wcount_reg = true, >> 1293 }; >> >> You may still say this should be in the DT, but the Tegra maintainers >> prefer this data in the driver. > > Okay I don't see a a rationale behind this not being in DT, Stephan? Let me know what you think of Stephen's feedback and if you are OK with this. >>>>>> + dma_cap_set(DMA_SLAVE, tdma->dma_dev.cap_mask); >>>>>> + dma_cap_set(DMA_PRIVATE, tdma->dma_dev.cap_mask); >>>>>> + dma_cap_set(DMA_CYCLIC, tdma->dma_dev.cap_mask); >>>>> >>>>> I think you should not set DMA_SLAVE, do you need caps to be exported. I >>>>> think that should be exported for cyclic too, let me know if that was the >>>>> issue? >>>>> >>>> >>>> Why should I not be setting DMA_SLAVE? Should I not be calling >>>> dma_get_any_slave_channel() in the xlate? >>>> >>>> I think that I do want to set DMA_CYCLIC as well to ensure that we check >>>> that the device->device_prep_dma_cyclic() function pointer is populated >>>> when registering the DMA controller. >>> >>> Only setting DMA_CYCLIC should do, if you see any issues around that please >>> get back, we cna fix those :) >> >> It did not work for me because dma_get_any_slave_channel() wants a DMA >> device with the DMA_SLAVE bit capability set. So if I remove this above, >> then requesting the channel fails via dma_get_any_slave_channel() fails. >> Is there something I don't understand here? > > You should use dma_request_channel() we cleaned up the APIs and recommend to > use dma_request_channel() for slave usages. See Documentation update in > a8135d0d79e9: (dmaengine: core: Introduce new, universal API to request a > channel) I had a look at this, but actually, I don't think this is going to work. Looking at dma_request_channel(), it is going to get a DMA channel that matches the mask for any DMA controller. In the xlate I already know which DMA controller I am and I just want one of the channels. The flow here is ... dma_request_chan() --> of_dma_request_slave_channel() --> xlate() --> dma_get_any_slave_channel() There are several other DMA drivers that are calling dma_get_any_slave_channel() from their xlate function which makes sense because they are requesting one of their own channels. I can understand that you wish to consolidate the APIs for requesting a channel, but it seems to me that you still need to have an API that DMA controller drivers can call where they can pass their dma_device structure to ensure you get a channel for the appropriate DMA controller. Cheers Jon -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html