> 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). 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(). Regards, Akhil
