linux-kernel - Re: [PATCH v5 09/13] soc: mediatek: cmdq: add write

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Date:   Mon, 25 May 2020 15:59:47 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Dennis-YC Hsieh <dennis-yc.hsieh@...iatek.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, devicetree@...r.kernel.org,
        wsd_upstream@...iatek.com, dri-devel@...ts.freedesktop.org,
        Bibby Hsieh <bibby.hsieh@...iatek.com>,
        CK Hu <ck.hu@...iatek.com>,
        Houlong Wei <houlong.wei@...iatek.com>,
        linux-arm-kernel@...ts.infradead.org,
        HS Liao <hs.liao@...iatek.com>
Subject: Re: [PATCH v5 09/13] soc: mediatek: cmdq: add write_s value function



On 25/05/2020 12:38, Dennis-YC Hsieh wrote:
> 
> On Mon, 2020-05-25 at 10:39 +0200, Matthias Brugger wrote:
>>
>> On 25/05/2020 04:27, Dennis-YC Hsieh wrote:
>>>
>>> On Sun, 2020-05-24 at 20:13 +0200, Matthias Brugger wrote:
>>>>
>>>> On 24/05/2020 19:31, Dennis-YC Hsieh wrote:
>>>>> Hi Matthias,
>>>>>
>>>>> Thanks for your comment.
>>>>>
>>>>> On Sat, 2020-05-16 at 20:20 +0200, Matthias Brugger wrote:
>>>>>>
>>>>>> On 08/03/2020 11:52, Dennis YC Hsieh wrote:
>>>>>>> add write_s function in cmdq helper functions which
>>>>>>> writes a constant value to address with large dma
>>>>>>> access support.
>>>>>>>
>>>>>>> Signed-off-by: Dennis YC Hsieh <dennis-yc.hsieh@...iatek.com>
>>>>>>> Reviewed-by: CK Hu <ck.hu@...iatek.com>
>>>>>>> ---
>>>>>>>  drivers/soc/mediatek/mtk-cmdq-helper.c | 26 ++++++++++++++++++++++++++
>>>>>>>  include/linux/soc/mediatek/mtk-cmdq.h  | 14 ++++++++++++++
>>>>>>>  2 files changed, 40 insertions(+)
>>>>>>>
>>>>>>> diff --git a/drivers/soc/mediatek/mtk-cmdq-helper.c b/drivers/soc/mediatek/mtk-cmdq-helper.c
>>>>>>> index 03c129230cd7..a9ebbabb7439 100644
>>>>>>> --- a/drivers/soc/mediatek/mtk-cmdq-helper.c
>>>>>>> +++ b/drivers/soc/mediatek/mtk-cmdq-helper.c
>>>>>>> @@ -269,6 +269,32 @@ int cmdq_pkt_write_s(struct cmdq_pkt *pkt, u16 high_addr_reg_idx,
>>>>>>>  }
>>>>>>>  EXPORT_SYMBOL(cmdq_pkt_write_s);
>>>>>>>  
>>>>>>> +int cmdq_pkt_write_s_value(struct cmdq_pkt *pkt, u16 high_addr_reg_idx,
>>>>>>> +			   u16 addr_low, u32 value, u32 mask)
>>>>>>> +{
>>>>>>> +	struct cmdq_instruction inst = { {0} };
>>>>>>> +	int err;
>>>>>>> +
>>>>>>> +	if (mask != U32_MAX) {
>>>>>>> +		inst.op = CMDQ_CODE_MASK;
>>>>>>> +		inst.mask = ~mask;
>>>>>>> +		err = cmdq_pkt_append_command(pkt, inst);
>>>>>>> +		if (err < 0)
>>>>>>> +			return err;
>>>>>>> +
>>>>>>> +		inst.op = CMDQ_CODE_WRITE_S_MASK;
>>>>>>> +	} else {
>>>>>>> +		inst.op = CMDQ_CODE_WRITE_S;
>>>>>>> +	}
>>>>>>> +
>>>>>>> +	inst.sop = high_addr_reg_idx;
>>>>>>
>>>>>> Writing u16 value in a 5 bit wide variable?
>>>>>
>>>>> We need only 5 bits in this case. I'll change high_addr_reg_idx
>>>>> parameter to u8.
>>>>>
>>>>
>>>> Ok, please make sure to mask the value, so that it's explicit in the code that
>>>> we only use the lowest 5 bits of high_addr_reg_idx.
>>>
>>> Is it necessary to mask the value?
>>> Since sop already defined as "u8 sop:5;", I thought it is explicit that
>>> only use 5 bits and compiler should do the rest jobs.
>>
>> Yes but it makes the code more explicit if we have a
>> inst.sop = high_addr_reg_idx & 0x1f;
>>
>> What do you think?
> 
> The value assign to sop will restrict by hardware spec. Clients call
> this function will define constant value and use it as parameter. So I
> think we don't worry about client call this api with wrong value.
> 

Ok, then let's change the parameter to u8 and don't add a mask.

Regards,
Matthias