On Wed, May 27, 2020 at 01:50:20AM +0300, Serge Semin wrote: > IP core of the DW DMA controller may be synthesized with different > max burst length of the transfers per each channel. According to Synopsis > having the fixed maximum burst transactions length may provide some > performance gain. At the same time setting up the source and destination > multi size exceeding the max burst length limitation may cause a serious > problems. In our case the DMA transaction just hangs up. In order to fix > this lets introduce the max burst length platform config of the DW DMA > controller device and don't let the DMA channels configuration code > exceed the burst length hardware limitation. > > Note the maximum burst length parameter can be detected either in runtime > from the DWC parameter registers or from the dedicated DT property. > Depending on the IP core configuration the maximum value can vary from > channel to channel so by overriding the channel slave max_burst capability > we make sure a DMA consumer will get the channel-specific max burst > length. ... > static void dwc_caps(struct dma_chan *chan, struct dma_slave_caps *caps) > { > + struct dw_dma_chan *dwc = to_dw_dma_chan(chan); > Perhaps, /* DesignWare DMA supports burst value from 0 */ caps->min_burst = 0; > + caps->max_burst = dwc->max_burst; > } ... > + *maxburst = clamp(*maxburst, 0U, dwc->max_burst); Shouldn't we do the same for iDMA 32-bit? Thus, perhaps do it in the core.c? > *maxburst = *maxburst > 1 ? fls(*maxburst) - 2 : 0; > + if (!of_property_read_u32_array(np, "snps,max-burst-len", mb, > + nr_channels)) { > + for (tmp = 0; tmp < nr_channels; tmp++) > + pdata->max_burst[tmp] = mb[tmp]; I think we may read directly to the array. This ugly loops were introduced due to type mismatch. (See below) > + } else { > + for (tmp = 0; tmp < nr_channels; tmp++) > + pdata->max_burst[tmp] = DW_DMA_MAX_BURST; > + } And this will be effectively memset32(). > unsigned char nr_masters; > unsigned char data_width[DW_DMA_MAX_NR_MASTERS]; > unsigned char multi_block[DW_DMA_MAX_NR_CHANNELS]; > + unsigned int max_burst[DW_DMA_MAX_NR_CHANNELS]; I think we have to stop with this kind of types and use directly what is in the properties, i.e. u32 max_burst[...]; -- With Best Regards, Andy Shevchenko