22.08.2022 13:29, Akhil R пишет: >> On 8/22/22 09:56, Akhil R wrote: >>>> 19.08.2022 18:15, Dmitry Osipenko пишет: >>>>> 19.08.2022 15:23, Akhil R пишет: >>>>>> if (of_device_is_compatible(np, "nvidia,tegra210-i2c-vi")) >>>>>> i2c_dev->is_vi = true; >>>>>> + else >>>>>> + i2c_dev->dma_support = !!(of_find_property(np, "dmas", >>>>>> + NULL)); >>>>> >>>>> 1. You leak the np returned by of_find_property(). >>>>> >>>>> 2. There is device_property_read_bool() for this kind of >>>>> property-exists checks. >>> Okay. I went by the implementation in of_dma_request_slave_channel() to >>> check 'dmas'. >>> >>>>> >>>>> 3. If "dmas" is missing in DT, then dma_request_chan() should return >>>>> NULL and everything will work fine. I suppose you haven't tried to >>>>> test this code. >>>> >>>> Although, no. It should return ERR_PTR(-ENODEV) and then you should check >>>> the return code. >>> Yes. Agree that it is more agnostic to check for ERR_PTR(-ENODEV). But since I >>> call tegra_init_dma() for every large transfer until DMA is initialized, wouldn't >>> it be better to have a flag inside the driver so that we do not have to go >> through >>> so many functions for every attempted DMA transaction to find out that the >> DT >>> properties don't exist? >>> >>> Shall I just put i2c_dev->dma_support = true here since DMA is supported by >>> hardware? It would turn false if dma_request_chan() returns something other >>> than -EPROBE_DEFER. >>> >>> if (of_device_is_compatible(np, "nvidia,tegra210-i2c-vi")) >>> i2c_dev->is_vi = true; >>> + else >>> + i2c_dev->dma_support = true; >> >> The code already has dma_mode for that. I don't see why another variable >> is needed. >> >> Either add new generic dma_request_chan_optional() that will return NULL >> if channel is not available and make Tegra I2C driver to use it, or >> handle the error code returned by dma_request_chan(). > > Let me elaborate my thoughts. > > The function tegra_i2c_init_dma() is also called inside tegra_i2c_xfer_msg() if > DMA is not initialized before, i.e. if (!i2c_dev->dma_buf). This is not true i2c_dev->dma_mode=false if !i2c_dev->dma_buf and that's it https://elixir.bootlin.com/linux/v6.0-rc2/source/drivers/i2c/busses/i2c-tegra.c#L1253 tegra_i2c_init_dma() is invoked only during probe > So, if suppose there is no DT entry for dmas, the driver would have to go take the > path tegra_i2c_init_dma() -> dma_request_chan() -> of_*() apis -> ... and then figure > out that DMA is not supported. This would happen for each transfer of size larger than > I2C_PIO_MODE_PREFERRED_LEN. > > To avoid this, I am looking for a variable/flag which can indicate if the driver should attempt > to configure DMA or not. I didn't quite get the idea if dma_mode can be extended to support > this, because it is updated based on xfer_size on each transfer. My idea of i2c_dev->dma_support > is that it will be constant after the probe().
