From mboxrd@z Thu Jan 1 00:00:00 1970 From: Fabrice Gasnier Subject: Re: [PATCH 4/8] mfd: stm32-timers: add support for dmas Date: Wed, 24 Jan 2018 09:40:36 +0100 Message-ID: <2e6afc46-9ad4-a858-29c7-692798ece82f@st.com> References: <1516106631-18722-1-git-send-email-fabrice.gasnier@st.com> <1516106631-18722-5-git-send-email-fabrice.gasnier@st.com> <20180123133234.xmep76cgdremnj47@dell> <20180123153035.2rvhspe2m5ej57op@dell> <20180123164121.xjzhypqe2u5c7zza@dell> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180123164121.xjzhypqe2u5c7zza@dell> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Lee Jones Cc: mark.rutland@arm.com, mcoquelin.stm32@gmail.com, alexandre.torgue@st.com, devicetree@vger.kernel.org, linux@armlinux.org.uk, robh+dt@kernel.org, linux-kernel@vger.kernel.org, thierry.reding@gmail.com, linux-pwm@vger.kernel.org, benjamin.gaignard@linaro.org, linux-arm-kernel@lists.infradead.org, benjamin.gaignard@st.com List-Id: devicetree@vger.kernel.org On 01/23/2018 05:41 PM, Lee Jones wrote: > On Tue, 23 Jan 2018, Fabrice Gasnier wrote: >> On 01/23/2018 04:30 PM, Lee Jones wrote: >>> On Tue, 23 Jan 2018, Fabrice Gasnier wrote: >>> >>>> On 01/23/2018 02:32 PM, Lee Jones wrote: >>>>> On Tue, 16 Jan 2018, Fabrice Gasnier wrote: >>>>> >>>>>> STM32 Timers can support up to 7 dma requests: >>>>>> 4 channels, update, compare and trigger. >>>>>> Optionally request part, or all dmas from stm32-timers MFD core. >>>>>> Also, keep reference of device's bus address to allow child drivers to >>>>>> transfer data from/to device by using dma. >>>>>> >>>>>> Signed-off-by: Fabrice Gasnier >>>>>> --- >>>>>> drivers/mfd/stm32-timers.c | 37 ++++++++++++++++++++++++++++++++++++- >>>>>> include/linux/mfd/stm32-timers.h | 14 ++++++++++++++ >>>>>> 2 files changed, 50 insertions(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/drivers/mfd/stm32-timers.c b/drivers/mfd/stm32-timers.c >>>>>> static int stm32_timers_probe(struct platform_device *pdev) >>>>>> { >>>>>> struct device *dev = &pdev->dev; >>>>>> @@ -44,6 +61,7 @@ static int stm32_timers_probe(struct platform_device *pdev) >>>>>> mmio = devm_ioremap_resource(dev, res); >>>>>> if (IS_ERR(mmio)) >>>>>> return PTR_ERR(mmio); >>>>>> + ddata->phys_base = res->start; >>>>> >>>>> What do you use this for? >>>> >>>> This is used in in child driver (pwm) for capture data transfer by dma. >>> >>> Might be worth being clear about that. >>> >>> Perhaps pass in 'dma_base' (phys_base + offset) instead? >> >> I guess you've had a look at [PATCH 5/8] pwm: stm32: add capture >> support. Are you talking about passing phys_base + TIM_DMAR ? > > I have and I am. > >> If this is the case, I'd prefer to keep phys base only if you don't >> mind, and handle TIM_DMAR offset in pwm driver. This way, all dma slave >> config is kept locally at one place. >> Or do you mean something else ? >> >> Maybe I can add a comment here about this ? >> Something like: >> /* phys_base to be used by child driver, e.g. DMA burst mode */ > > I haven't seen the memory map for this device, so it's not easy for me > to comment, but passing in the physical address of the parent MFD into > a child device doesn't quite sit right with me. > > At what level does TIM_DMAR sit? Is it a child (PWM) specific > property, or is it described at parent (Timer) level? > Hi Lee, This isn't child (PWM) specific. TIM_DMAR is described at timer level as well as all timers DMA requests lines. Current patchset make it useful for PWM capture. Basically, I think this can be seen as interrupts, as each (0..7) dma request has an enable bit (in DIER: interrupt enable register). This is similar as interrupts at timer level. So, I understand your point regarding passing physical address of the parent MFD... Speaking of interrupts, I'd probably have looked at irq_chip. Regarding dma, i'm not sure what is preferred way ? Another way maybe to export a routine (export symbol) from MFD core, to handle dma transfer from there? By looking into drivers/mfd, I found similar approach, e.g. rtsx_pci_dma_transfer(). Do you think this is better approach ? Please let me know your opinion. Best Regards, Fabrice