Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [RESEND PATCH v2 4/8] mfd: stm32-timers: add support for dmas
To:     Lee Jones <lee.jones@linaro.org>
CC:     <thierry.reding@gmail.com>, <alexandre.torgue@st.com>,
        <benjamin.gaignard@linaro.org>, <robh+dt@kernel.org>,
        <mark.rutland@arm.com>, <linux@armlinux.org.uk>,
        <mcoquelin.stm32@gmail.com>, <benjamin.gaignard@st.com>,
        <devicetree@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux-pwm@vger.kernel.org>
References: <1518602679-3064-1-git-send-email-fabrice.gasnier@st.com>
 <1518602679-3064-5-git-send-email-fabrice.gasnier@st.com>
 <20180328152251.xeh72dpeflzohn4k@dell>
 <106ff518-4973-5d4a-b5bf-dd58cbd8439a@st.com>
 <20180329125912.jgasmw75qvtlszgx@dell>
From:   Fabrice Gasnier <fabrice.gasnier@st.com>
Message-ID: <12d53b2e-eec4-a498-1e1f-c217161c5086@st.com>
Date:   Thu, 29 Mar 2018 15:41:24 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
MIME-Version: 1.0
In-Reply-To: <20180329125912.jgasmw75qvtlszgx@dell>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 03/29/2018 02:59 PM, Lee Jones wrote:
> On Wed, 28 Mar 2018, Fabrice Gasnier wrote:
> 
>> On 03/28/2018 05:22 PM, Lee Jones wrote:
>>> On Wed, 14 Feb 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 add routine to implement burst reads using DMA from timer registers.
>>>> This is exported. So, it can be used by child drivers, PWM capture
>>>> for instance (but not limited to).
>>>>
>>>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
>>>> Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
>>>> ---
>>>> Changes in v2:
>>>> - Abstract DMA handling from child driver: move it to MFD core
>>>> - Add comments on optional dma support
>>>> ---
>>>>  drivers/mfd/stm32-timers.c       | 215 ++++++++++++++++++++++++++++++++++++++-
>>>>  include/linux/mfd/stm32-timers.h |  27 +++++
>>>>  2 files changed, 238 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/mfd/stm32-timers.c b/drivers/mfd/stm32-timers.c
>>>> index a6675a4..2cdad2c 100644
>>>> --- a/drivers/mfd/stm32-timers.c
>>>> +++ b/drivers/mfd/stm32-timers.c
> 
> [...]
> 
>>>> +	struct dma_chan *dmas[STM32_TIMERS_MAX_DMAS];
>>>> +	struct stm32_timers ddata;
>>>
>>> This looks odd to me.  Why can't you expand the current ddata
>>> structure?  Wouldn't it be better to create a stm32_timers_dma
>>> structure to place all this information in (except *dev, that should
>>> live in the ddata struct), then place a reference in the existing
>>> stm32_timers struct?
>>
>> Maybe I miss-understand you here, from what we discussed in V1:
>> https://lkml.org/lkml/2018/1/23/574
>>> ... "passing in the physical address of the parent MFD into
>>> a child device doesn't quite sit right with me"
>> I introduced this private struct in MFD parent, and completely hide it
>> from the child.
>>
>> So, do you suggest to add struct definition here ? But make it part of
>> struct stm32_timers *ddata?
>>
>> And only put declaration in include/linux/mfd/stm32-timers.h:
>> + struct stm32_timers_dma;
>>
>> struct stm32_timers {
>> 	struct clk *clk;
>> 	struct regmap *regmap;
>> 	u32 max_arr;
>> +	struct stm32_timers_dma;
>> };
> 
> Yes, that's the basic idea.
> 
>> I can probably spare the *dev then... use dev->parent in child driver.
> 
> What would you use dev->parent for?

Hi Lee,

This is to follow your sugestion to use *dev instead of *ddata when
calling stm32_timers_dma_burst_read(), the idea is to use it on child side:
stm32_timers_dma_burst_read(dev->parent,...) from pwm driver.
Then there is no need to keep *dev inside ddata struct.

> 
> [...]
> 
>>>> +static int stm32_timers_remove(struct platform_device *pdev)
>>>> +{
>>>> +	struct stm32_timers *ddata = platform_get_drvdata(pdev);
>>>> +	struct stm32_timers_priv *priv = to_stm32_timers_priv(ddata);
>>>> +
>>>> +	of_platform_depopulate(&pdev->dev);
>>>
>>> Why can't you continue using devm_*?
>>
>> I can use devm_of_platform_depopulate() here if you prefer, and keep
>> devm_of_platform_populate() in probe.
> 
> The point of devm_* is that you don't have to call depopulate.
> 
> It happens automatically once this driver is unbound.

Ok, so to clarify, keeping devm_ here may be a bit racy:
of_platform_depopulate will happen after dma has been released (there is
no devm_ variant to release dma).
Only way to prevent race condition here, is to enforce
of_platform_depopulate() is called before dma release (e.g. in reverse
order compared to probe).

Do you wish I add a comment about it ?

Best Regards,
Fabrice

>