From mboxrd@z Thu Jan 1 00:00:00 1970 From: lee.jones@linaro.org (Lee Jones) Date: Mon, 15 Apr 2013 12:59:06 +0100 Subject: [PATCH 3/8] dmaengine: ste_dma40: Actually write the runtime configuration to registers In-Reply-To: References: <1365532783-27425-1-git-send-email-lee.jones@linaro.org> <1365532783-27425-3-git-send-email-lee.jones@linaro.org> <20130415110601.GE6512@gmail.com> Message-ID: <20130415115906.GF6512@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, 15 Apr 2013, Rabin Vincent wrote: > 2013/4/15 Lee Jones : > > On Fri, 12 Apr 2013, Rabin Vincent wrote: > >> 2013/4/9 Lee Jones : > >> > Someone has spent a fair amount of effort writing a runtime configuration > >> > changing algorithm for DMA clients. However, the config appears to never > >> > actually make it to hardware. In order for the configuration to take hold > >> > we need to issue a d40_config_write(), as this is the routine which writes > >> > it into the hardware's registers. > >> > >> No, it's not. This function is only for initial configuration which > >> should only be written when the channel is allocated. In fact, by > >> calling it here in runtime_config, you are introducing a serious bug: > >> other logical channels on the same physical channel will stop because of > >> the SSLNK/SDLNK of the physical channel being zeroed. > >> > >> The runtime config already makes it the hardware in the existing code, > >> via d40_*_cfg(). > > > > Sorry Rabin, but the only place I can see the config being written is > > in d40_config_write(). > > > > Can you paste the line of code in d40_*_cfg() which actually writes > > the config to hardware please? I don't see it. > > It's not that simple. There are some pointers passed to d40_*_cfg() and > that function writes the configuration to the variables those pointers > point to (d40c->log_def.lcsp1, d40c->src_def_cfg, etc.). Please read > the code to see how those variables end up being used later when the > LLIs are prepared for the HW. I have read the code, which is why I know that the config only gets written in d40_config_write(). :) So the configuration which gets set in the runtime_config routine doesn't ever make it to hardware - hence this patch. Unless I'm missing something? -- Lee Jones Linaro ST-Ericsson Landing Team Lead Linaro.org ? Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog