> 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. What I am trying for is to have a mechanism that doesn't halt the i2c transfers till DMA is available. Also, I do not want to drop DMA because it was unavailable during probe(). This situation is sure to hit if we have I2C driver as built in and DMA driver as a module. In such cases, I2C will never be able to use the DMA. Another option I thought about was to request and free DMA channel for each transfer, which many serial drivers already do. But I am a bit anxious if that will increase the latency of transfer. Regards, Akhil
