From mboxrd@z Thu Jan 1 00:00:00 1970 From: Horng-Shyang Liao Subject: Re: [PATCH v8 2/3] CMDQ: Mediatek CMDQ driver Date: Fri, 17 Jun 2016 16:28:27 +0800 Message-ID: <1466152107.11184.14.camel@mtksdaap41> References: <1464578397-29743-1-git-send-email-hs.liao@mediatek.com> <1464578397-29743-3-git-send-email-hs.liao@mediatek.com> <574C5CBF.7060002@gmail.com> <1464683762.14604.59.camel@mtksdaap41> <574DEE40.9010008@gmail.com> <1464775020.11122.40.camel@mtksdaap41> <574FF264.7050209@gmail.com> <1464934356.15175.31.camel@mtksdaap41> <57516774.5080008@gmail.com> <1464956037.16029.8.camel@mtksdaap41> <575181E5.6090603@gmail.com> <5756FD73.3050607@gmail.com> <1465364427.9963.13.camel@mtksdaap41> <5757F762.4020908@gmail.com> <1465388727.21326.8.camel@mtksdaap41> <57583B45.2080504@gmail.com> <1465890268.7191.13.camel@mtksdaap41> <575FD9BA.8040708@gmail.com> <1465906063.20796.20.camel@mtksdaap41> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1465906063.20796.20.camel@mtksdaap41> Sender: linux-kernel-owner@vger.kernel.org To: Matthias Brugger Cc: Rob Herring , Daniel Kurtz , Sascha Hauer , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, srv_heupstream@mediatek.com, Sascha Hauer , Philipp Zabel , Nicolas Boichat , CK HU , cawa cheng , Bibby Hsieh , YT Shen , Daoyuan Huang , Damon Chu , Josh-YC Liu , Glory Hung , Jiaguang Zhang , Dennis-YC Hsieh , Monica Wang , jassisinghbrar@gmail.com, jaswinder. List-Id: devicetree@vger.kernel.org Hi Matthias, On Tue, 2016-06-14 at 20:07 +0800, Horng-Shyang Liao wrote: > Hi Matthias, > > On Tue, 2016-06-14 at 12:17 +0200, Matthias Brugger wrote: > > > > On 14/06/16 09:44, Horng-Shyang Liao wrote: > > > Hi Matthias, > > > > > > On Wed, 2016-06-08 at 17:35 +0200, Matthias Brugger wrote: > > >> > > >> On 08/06/16 14:25, Horng-Shyang Liao wrote: > > >>> Hi Matthias, > > >>> > > >>> On Wed, 2016-06-08 at 12:45 +0200, Matthias Brugger wrote: > > >>>> > > >>>> On 08/06/16 07:40, Horng-Shyang Liao wrote: > > >>>>> Hi Matthias, > > >>>>> > > >>>>> On Tue, 2016-06-07 at 18:59 +0200, Matthias Brugger wrote: > > >>>>>> > > >>>>>> On 03/06/16 15:11, Matthias Brugger wrote: > > >>>>>>> > > >>>>>>> > > >>>>>> [...] > > >>>>>> > > >>>>>>>>>>>>>>>> + > > >>>>>>>>>>>>>>>> + smp_mb(); /* modify jump before enable thread */ > > >>>>>>>>>>>>>>>> + } > > >>>>>>>>>>>>>>>> + > > >>>>>>>>>>>>>>>> + cmdq_thread_writel(thread, task->pa_base + > > >>>>>>>>>>>>>>>> task->command_size, > > >>>>>>>>>>>>>>>> + CMDQ_THR_END_ADDR); > > >>>>>>>>>>>>>>>> + cmdq_thread_resume(thread); > > >>>>>>>>>>>>>>>> + } > > >>>>>>>>>>>>>>>> + list_move_tail(&task->list_entry, &thread->task_busy_list); > > >>>>>>>>>>>>>>>> + spin_unlock_irqrestore(&cmdq->exec_lock, flags); > > >>>>>>>>>>>>>>>> +} > > >>>>>>>>>>>>>>>> + > > >>>>>>>>>>>>>>>> +static void cmdq_handle_error_done(struct cmdq *cmdq, > > >>>>>>>>>>>>>>>> + struct cmdq_thread *thread, u32 irq_flag) > > >>>>>>>>>>>>>>>> +{ > > >>>>>>>>>>>>>>>> + struct cmdq_task *task, *tmp, *curr_task = NULL; > > >>>>>>>>>>>>>>>> + u32 curr_pa; > > >>>>>>>>>>>>>>>> + struct cmdq_cb_data cmdq_cb_data; > > >>>>>>>>>>>>>>>> + bool err; > > >>>>>>>>>>>>>>>> + > > >>>>>>>>>>>>>>>> + if (irq_flag & CMDQ_THR_IRQ_ERROR) > > >>>>>>>>>>>>>>>> + err = true; > > >>>>>>>>>>>>>>>> + else if (irq_flag & CMDQ_THR_IRQ_DONE) > > >>>>>>>>>>>>>>>> + err = false; > > >>>>>>>>>>>>>>>> + else > > >>>>>>>>>>>>>>>> + return; > > >>>>>>>>>>>>>>>> + > > >>>>>>>>>>>>>>>> + curr_pa = cmdq_thread_readl(thread, CMDQ_THR_CURR_ADDR); > > >>>>>>>>>>>>>>>> + > > >>>>>>>>>>>>>>>> + list_for_each_entry_safe(task, tmp, &thread->task_busy_list, > > >>>>>>>>>>>>>>>> + list_entry) { > > >>>>>>>>>>>>>>>> + if (curr_pa >= task->pa_base && > > >>>>>>>>>>>>>>>> + curr_pa < (task->pa_base + task->command_size)) > > >>>>>>>>>>>>>>> > > >>>>>>>>>>>>>>> What are you checking here? It seems as if you make some implcit > > >>>>>>>>>>>>>>> assumptions about pa_base and the order of execution of > > >>>>>>>>>>>>>>> commands in the > > >>>>>>>>>>>>>>> thread. Is it save to do so? Does dma_alloc_coherent give any > > >>>>>>>>>>>>>>> guarantees > > >>>>>>>>>>>>>>> about dma_handle? > > >>>>>>>>>>>>>> > > >>>>>>>>>>>>>> 1. Check what is the current running task in this GCE thread. > > >>>>>>>>>>>>>> 2. Yes. > > >>>>>>>>>>>>>> 3. Yes, CMDQ doesn't use iommu, so physical address is continuous. > > >>>>>>>>>>>>>> > > >>>>>>>>>>>>> > > >>>>>>>>>>>>> Yes, physical addresses might be continous, but AFAIK there is no > > >>>>>>>>>>>>> guarantee that the dma_handle address is steadily growing, when > > >>>>>>>>>>>>> calling > > >>>>>>>>>>>>> dma_alloc_coherent. And if I understand the code correctly, you > > >>>>>>>>>>>>> use this > > >>>>>>>>>>>>> assumption to decide if the task picked from task_busy_list is > > >>>>>>>>>>>>> currently > > >>>>>>>>>>>>> executing. So I think this mecanism is not working. > > >>>>>>>>>>>> > > >>>>>>>>>>>> I don't use dma_handle address, and just use physical addresses. > > >>>>>>>>>>>> From CPU's point of view, tasks are linked by the busy list. > > >>>>>>>>>>>> From GCE's point of view, tasks are linked by the JUMP command. > > >>>>>>>>>>>> > > >>>>>>>>>>>>> In which cases does the HW thread raise an interrupt. > > >>>>>>>>>>>>> In case of error. When does CMDQ_THR_IRQ_DONE get raised? > > >>>>>>>>>>>> > > >>>>>>>>>>>> GCE will raise interrupt if any task is done or error. > > >>>>>>>>>>>> However, GCE is fast, so CPU may get multiple done tasks > > >>>>>>>>>>>> when it is running ISR. > > >>>>>>>>>>>> > > >>>>>>>>>>>> In case of error, that GCE thread will pause and raise interrupt. > > >>>>>>>>>>>> So, CPU may get multiple done tasks and one error task. > > >>>>>>>>>>>> > > >>>>>>>>>>> > > >>>>>>>>>>> I think we should reimplement the ISR mechanism. Can't we just read > > >>>>>>>>>>> CURR_IRQ_STATUS and THR_IRQ_STATUS in the handler and leave > > >>>>>>>>>>> cmdq_handle_error_done to the thread_fn? You will need to pass > > >>>>>>>>>>> information from the handler to thread_fn, but that shouldn't be an > > >>>>>>>>>>> issue. AFAIK interrupts are disabled in the handler, so we should stay > > >>>>>>>>>>> there as short as possible. Traversing task_busy_list is expensive, so > > >>>>>>>>>>> we need to do it in a thread context. > > >>>>>>>>>> > > >>>>>>>>>> Actually, our initial implementation is similar to your suggestion, > > >>>>>>>>>> but display needs CMDQ to return callback function very precisely, > > >>>>>>>>>> else display will drop frame. > > >>>>>>>>>> For display, CMDQ interrupt will be raised every 16 ~ 17 ms, > > >>>>>>>>>> and CMDQ needs to call callback function in ISR. > > >>>>>>>>>> If we defer callback to workqueue, the time interval may be larger than > > >>>>>>>>>> 32 ms.sometimes. > > >>>>>>>>>> > > >>>>>>>>> > > >>>>>>>>> I think the problem is, that you implemented the workqueue as a ordered > > >>>>>>>>> workqueue, so there is no parallel processing. I'm still not sure why > > >>>>>>>>> you need the workqueue to be ordered. Can you please explain. > > >>>>>>>> > > >>>>>>>> The order should be kept. > > >>>>>>>> Let me use mouse cursor as an example. > > >>>>>>>> If task 1 means move mouse cursor to point A, task 2 means point B, > > >>>>>>>> and task 3 means point C, our expected result is A -> B -> C. > > >>>>>>>> If the order is not kept, the result could become A -> C -> B. > > >>>>>>>> > > >>>>>>> > > >>>>>>> Got it, thanks for the clarification. > > >>>>>>> > > >>>>>> > > >>>>>> I think a way to get rid of the workqueue is to use a timer, which gets > > >>>>>> programmed to the time a timeout in the first task in the busy list > > >>>>>> would happen. Everytime we update the busy list (e.g. because of task > > >>>>>> got finished by the thread), we update the timer. When the timer > > >>>>>> triggers, which hopefully won't happen too often, we return timeout on > > >>>>>> the busy list elements, until the time is lower then the actual time. > > >>>>>> > > >>>>>> At least with this we can reduce the data structures in this driver and > > >>>>>> make it more lightweight. > > >>>>> > > >>>>> From my understanding, your proposed method can handle timeout case. > > >>>>> > > >>>>> However, the workqueue is also in charge of releasing tasks. > > >>>>> Do you take releasing tasks into consideration by using the proposed > > >>>>> timer method? > > >>>>> Furthermore, I think the code will become more complex if we also use > > >>>>> timer to implement releasing tasks. > > >>>>> > > >>>> > > >>>> Can't we call > > >>>> clk_disable_unprepare(cmdq->clock); > > >>>> cmdq_task_release(task); > > >>>> after invoking the callback? After I put clk_disable_unprepare(cmdq->clock) into ISR, I encounter another BUG. (Quote some Linux 4.7 source code.) 605 void clk_unprepare(struct clk *clk) 606 { 607 if (IS_ERR_OR_NULL(clk)) 608 return; 609 610 clk_prepare_lock(); // <-- Here 611 clk_core_unprepare(clk->core); 612 clk_prepare_unlock(); 613 } 614 EXPORT_SYMBOL_GPL(clk_unprepare); 91 static void clk_prepare_lock(void) 92 { 93 if (!mutex_trylock(&prepare_lock)) { // <-- Here 94 if (prepare_owner == current) { 95 prepare_refcnt++; 96 return; 97 } 98 mutex_lock(&prepare_lock); 99 } 100 WARN_ON_ONCE(prepare_owner != NULL); 101 WARN_ON_ONCE(prepare_refcnt != 0); 102 prepare_owner = current; 103 prepare_refcnt = 1; 104 } So, 'unprepare' can sleep and cannot be put into ISR. I also try to put it into a timer, but the error is the same since timer callback is executed by softirq. We need clk_disable_unprepare() since it can save power consumption in idle. Therefore, I plan to (1) move releasing buffer and task into ISR, (2) move timeout into timer, and (3) keep workqueue for clk_disable_unprepare(). What do you think? Thanks, HS > > >>> > > >>> Do you mean just call these two functions in ISR? > > >>> My major concern is dma_free_coherent() and kfree() in > > >>> cmdq_task_release(task). > > >> > > >> Why do we need the dma calls at all? Can't we just calculate the > > >> physical address using __pa(x)? > > > > > > I prefer to use dma_map_single/dma_unmap_single. > > > > > > > Can you please elaborate why you need this. We don't do dma, so we > > should not use dma memory for this. > > We need a buffer to share between CPU and GCE, so we do need DMA. > CPU is in charge of writing GCE commands into this buffer. > GCE is in charge of reading and running GCE commands from this buffer. > When we chain CMDQ tasks, we also need to modify GCE JUMP command. > Therefore, I prefer to use dma_alloc_coherent and dma_free_coherent. > > However, if we want to use timer to handle timeout, we need to release > memory in ISR. > In this case, using kmalloc/kfree + dma_map_single/dma_unmap_single > instead of dma_alloc_coherent/dma_free_coherent is an alternative > solution, but taking care the synchronization between cache and memory > is the expected overhead. > > > >>> Therefore, your suggestion is to use GFP_ATOMIC for both > > >>> dma_alloc_coherent() and kzalloc(). Right? > > >> > > >> I don't think we need GFP_ATOMIC, the critical path will just free the > > >> memory. > > > > > > I tested these two functions, and kfree was safe. > > > However, dma_free_coherent raised BUG. > > > BUG: failure at > > > /mnt/host/source/src/third_party/kernel/v3.18/mm/vmalloc.c:1514/vunmap()! > > > > Just a general hint. Please try to evaluate on a recent kernel. It looks > > like as if you tried this on a v3.18 based one. > > This driver should be backward compatible to v3.18 for a MTK project. > > > Best regards, > > Matthias > > Thanks, > HS > > > > 1512 void vunmap(const void *addr) > > > 1513 { > > > 1514 BUG_ON(in_interrupt()); // <-- here > > > 1515 might_sleep(); > > > 1516 if (addr) > > > 1517 __vunmap(addr, 0); > > > 1518 } > > > 1519 EXPORT_SYMBOL(vunmap); > > > > > > Therefore, I plan to use kmalloc + dma_map_single instead of > > > dma_alloc_coherent, and dma_unmap_single + kfree instead of > > > dma_free_coherent. > > > > > > What do you think about the function replacement? > > > > > >>> If so, I can try to implement timeout by timer, and discuss with you > > >>> if I have further questions. > > >>> > > >> > > >> Sounds good :) > > >> > > >> Thanks, > > >> Matthias > > > > > > Thanks, > > > HS > > > > > >>>> Regrading the clock, wouldn't it be easier to handle the clock > > >>>> enable/disable depending on the state of task_busy_list? I suppose we > > >>>> can't as we would need to check the task_busy_list of all threads, right? > > >>>> > > >>>> Regards, > > >>>> Matthias > > >>> > > >>> Thanks, > > >>> HS > > >>> > > > > > > > >