22.08.2022 23:33, Dmitry Osipenko пишет: > 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(). I see now that it's you added tegra_i2c_init_dma() to tegra_i2c_xfer_msg(). And tegra_i2c_init_dma() already falls back to PIO if DMA is unavailable. I don't remember why !IS_ENABLED(CONFIG_TEGRA20_APB_DMA) was added to tegra_i2c_init_dma(), but if dma_request_chan() returns -EPROBE_DEFER when there is no DMA channel available at all, then you should fix it. Trying to initialize DMA during transfer if it failed to initialize during probe is a wrong approach. DMA must be initialized only once during probe. Please make the probe to work properly.
