Hi Vinod, > -----Original Message----- > From: Vinod Koul [mailto:vinod.koul@xxxxxxxxx] > Sent: Wednesday, November 11, 2015 4:25 PM > To: Appana Durga Kedareswara Rao > Cc: dan.j.williams@xxxxxxxxx; Michal Simek; Soren Brinkmann; > moritz.fischer@xxxxxxxxx; anirudha@xxxxxxxxxx; dmaengine@xxxxxxxxxxxxxxx; > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Anirudha > Sarangi; Punnaiah Choudary Kalluri > Subject: Re: [PATCH v9] dmaengine: Add Xilinx AXI Direct Memory Access Engine > driver support > > On Tue, Nov 10, 2015 at 10:23:35AM +0000, Appana Durga Kedareswara Rao > wrote: > > > > > Pls justify why we should have two drivers. Looking at code > > > > > makes me think otherwise > > > > > > > > > > > [pls wrap your messages within 80 chars, I have reflowed below] > > And ignoring recommendations does not help!! Sorry for the noise will fix it next time on wards... > > > > > > I agree with you and even initially we had a common driver with > > > > the similar implementation as you were mentioning. Later on, > > > > being soft IPs, new features were added and the IPs became > > > > diversified. As an example, this driver has a residue Calculation > > > > whereas the other driver (VDMA) is not applicable and the way interrupts > are handled is completely different. > > > > Briefly, they are two complete different IPs with a different > > > > register set and descriptor format. Eventually, it became too > > > > complex To manage the common driver as the code became messy with > lot of conditions around. > > > > Mainly the validation process is a big concern, as every change In > > > > the IP compels to test all the complete features of both IPs. So, > > > > we got convinced to the approach of separating the drivers to > > > > overcome this and it comes with Few addition lines of common code. > > > > > > No it is not that hard, bunch of people already do that. > > > > > > You need is a smart probe or perhaps invoke IP specfic method to > > > initialize dma controller. > > > > > > In above case no one forces you to register status callback for > > > both, you can do based on the controller probed... > > > > > > I am sorry but validation is not a strong point here. I have a > > > driver which manages bunch of different generations. Reuse helps in > > > having lesser code and bug fixes across generations easily.. > > > > > > We cant have two drivers pretty much doing same thing in kernel > > > > > > Please fix this and come back > > > > Sorry for delayed response. I was out sick. > > I had internal discussions with my team. Both DMA's target for completely > different use cases, have different register sets and different descriptor formats. > Interrupt processing is also different. Each of these IPs undergo frequent > changes and enhancements. Having a single driver means for any small change > in any of the IPs the testing has to happen across a whole lot of test cases which > looks inefficient. > > Thinking futuristically where we don't know in which way the IP changes can > happen, I feel it is always good to have separate drivers. We can't predict the > HW changes and since the DMAs are targeted for different use cases, we may > end up in tricky situations if we have a single driver. > > I do agree that code reuse is generally efficient. But for our case we are not > dealing with generations of same IP, but completely different IPs. Though there > are some similarities between them, I feel the differences are many. > > On v7 of this series, I had put the same observation to which you seem to have > agreed. That is the reason I went ahead with other comments. At this point it is > definitely really hard for me to merge. > > Lot of this is unreadable and I am not going to add effort on this > > > However, if you still insist and see a lot of value in having a single driver, I will > see what I can do. As I said, it will be some work and in long term it will be a > maintenance issue for Xilinx and our customers. > > Yes please, I know you will have arguments for it but we know reuse helps, > reduces bugs. Yes validation is increased but that is how drivers are written and > maintained, and pls automate that! Sure will come back with a patch by merging the two drivers soon. Regards, Kedar. > > -- > ~Vinod -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
