linux-kernel - Re: [Freedreno] [PATCH v6 2/6] clk: qcom: Allow custom reset ops

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Date:   Fri, 2 Sep 2022 01:20:40 +0530
From:   Akhil P Oommen <quic_akhilpo@...cinc.com>
To:     Philipp Zabel <p.zabel@...gutronix.de>
CC:     Stephen Boyd <sboyd@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Douglas Anderson <dianders@...omium.org>,
        <dri-devel@...ts.freedesktop.org>,
        Stephen Boyd <swboyd@...omium.org>,
        <krzysztof.kozlowski@...aro.org>, Rob Clark <robdclark@...il.com>,
        Andy Gross <agross@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        <linux-clk@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [Freedreno] [PATCH v6 2/6] clk: qcom: Allow custom reset ops

On 9/1/2022 3:47 PM, Philipp Zabel wrote:
> Hi Akhil,
>
> On Wed, Aug 31, 2022 at 10:48:23AM +0530, Akhil P Oommen wrote:
>> Allow soc specific clk drivers to specify a custom reset operation. We
>> will use this in an upcoming patch to allow gpucc driver to specify a
>> differet reset operation for cx_gdsc.
>>
>> Signed-off-by: Akhil P Oommen <quic_akhilpo@...cinc.com>
>> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>> ---
>>
>> (no changes since v3)
>>
>> Changes in v3:
>> - Use pointer to const for "struct qcom_reset_ops" in qcom_reset_map (Krzysztof)
>>
>> Changes in v2:
>> - Return error when a particular custom reset op is not implemented. (Dmitry)
>>
>>   drivers/clk/qcom/reset.c | 27 +++++++++++++++++++++++++++
>>   drivers/clk/qcom/reset.h |  8 ++++++++
>>   2 files changed, 35 insertions(+)
>>
>> diff --git a/drivers/clk/qcom/reset.c b/drivers/clk/qcom/reset.c
>> index 819d194..b7ae4a3 100644
>> --- a/drivers/clk/qcom/reset.c
>> +++ b/drivers/clk/qcom/reset.c
>> @@ -13,6 +13,21 @@
>>   
>>   static int qcom_reset(struct reset_controller_dev *rcdev, unsigned long id)
>>   {
>> +	struct qcom_reset_controller *rst;
>> +	const struct qcom_reset_map *map;
>> +
>> +	rst = to_qcom_reset_controller(rcdev);
>> +	map = &rst->reset_map[id];
>> +
>> +	if (map->ops && map->ops->reset)
>> +		return map->ops->reset(map->priv);
>> +	/*
>> +	 * If custom ops is implemented but just not this callback, return
>> +	 * error
>> +	 */
>> +	else if (map->ops)
>> +		return -EOPNOTSUPP;
>> +
> It doesn't seem necessary to stack reset_ops -> qcom_reset_ops for what
> you need here.
> Just add an optional const struct reset_ops * to qcom_cc_desc and feed
> that into qcom_cc_really_probe to replace &qcom_reset_ops.
>
> [...]
>> +struct qcom_reset_ops {
>> +	int (*reset)(void *priv);
>> +	int (*assert)(void *priv);
>> +	int (*deassert)(void *priv);
> Why add assert and deassert ops? There doesn't seem to be any user.
I had a more minimal implementation in v1. But this makes it more 
complete and make it less prone to trip up ourselves in future.
>
>> +};
>> +
>>   struct qcom_reset_map {
>>   	unsigned int reg;
>>   	u8 bit;
>> +	const struct qcom_reset_ops *ops;
>> +	void *priv;
> Adding per-reset ops + priv counters seems excessive to me.
>
> Are you expecting different reset controls in the same reset controller
> to have completely different ops at some point? If so, I would wonder
> whether it wouldn't be better to split the reset controller in that
> case. Either way, for the GDSC collapse workaround this does not seem
> to be required at all.
Yes, like I responded in patch 4, we need different ops for the same 
reset controller in some gpucc implementations.
For eg: 
https://elixir.bootlin.com/linux/v6.0-rc3/source/drivers/clk/qcom/gpucc-sdm660.c

-Akhil
>
> regards
> Philipp