linux-kernel - Re: [PATCH v2] dmaengine: tegra-apb: proper default init of channel slave

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Date:	Fri, 22 Apr 2016 15:40:10 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Shardar Mohammed <smohammed@...dia.com>,
	Laxman Dewangan <ldewangan@...dia.com>,
	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"thierry.reding@...il.com" <thierry.reding@...il.com>,
	"gnurou@...il.com" <gnurou@...il.com>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] dmaengine: tegra-apb: proper default init of channel
 slave_id


On 22/04/16 14:56, Shardar Mohammed wrote:
> Thanks for the review, please check my comments inline in [Shardar].
> 
>> On 22/04/16 13:44, Shardar Shariff Md wrote:
>>> Initialize default channel slave_id(req_sel) to invalid id (i.e max
>>> supported slave id + 1) to avoid overwriting of slave_id during
>>> tegra_dma_slave_config() with client data if slave_id is not
>>> initialized through DT
>>>
>>> Signed-off-by: Shardar Shariff Md <smohammed@...dia.com>
>>>
>>> ---
>>> - Instead of initializing the slave id to -1 define macros for
>>>   max slave id and invalid slave id and do the checks accordingly.
>>> ---
>>>  drivers/dma/tegra20-apb-dma.c | 13 +++++++++++--
>>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/dma/tegra20-apb-dma.c
>>> b/drivers/dma/tegra20-apb-dma.c index 3871f29..2957e26 100644
>>> --- a/drivers/dma/tegra20-apb-dma.c
>>> +++ b/drivers/dma/tegra20-apb-dma.c
>>> @@ -114,6 +114,9 @@
>>>  /* Channel base address offset from APBDMA base address */
>>>  #define TEGRA_APBDMA_CHANNEL_BASE_ADD_OFFSET	0x1000
>>>
>>> +#define TEGRA_APBDMA_SLAVE_ID_MAX		31
>>
>> Sorry, thinking about this some more, given that the ID is programmed into a
>> field in the CSR register could we just define as mask here for the CSR field ...
>>
>> #define TEGRA_APBDMA_CSR_REQ_SEL_MASK	0x1f
>>
>> Note this should be defined with the other CSR register field definitions.
> [Shardar] Will take care of it. One doubt do you mean below.
> Will define this with other CSR register fields.
> #define TEGRA_APBDMA_CSR_REQ_SEL_MASK	0x1f
> 
> #define TEGRA_APBDMA_SLAVE_ID_MAX		TEGRA_APBDMA_CSR_REQ_SEL_MASK

We don't need the MAX definition as well.

>>
>>> +#define TEGRA_APBDMA_SLAVE_ID_INVALID
>> 	(TEGRA_APBDMA_SLAVE_ID_MAX + 1)
>>>
>>>  struct tegra_dma;
>>>
>>>  /*
>>> @@ -353,7 +356,7 @@ static int tegra_dma_slave_config(struct dma_chan
>> *dc,
>>>  	}
>>>
>>>  	memcpy(&tdc->dma_sconfig, sconfig, sizeof(*sconfig));
>>> -	if (!tdc->slave_id)
>>> +	if (tdc->slave_id == TEGRA_APBDMA_SLAVE_ID_INVALID)
>>>  		tdc->slave_id = sconfig->slave_id;
>>
>> I believe I mentioned before that here we should ...
>>
>> 	if (tdc->slave_id != TEGRA_APBDMA_SLAVE_ID_INVALID)
>> 		return -EBUSY;
> 
> [Shardar] By the time this function tegra_dma_slave_config is called, slave_id here is already initialized through DT(provided option) through function tegra_dma_of_xlate().
> And filling up the slave id here from sconfig structure that is provided by dma client driver is used here if it dma client is not initialized through DT. 
> Please correct me if am wrong.

Yes you are right. So on further inspection this allows the user to set
the slave ID if it is not set yet. So I think we need ...

	if (tdc->slave_id == TEGRA_APBDMA_SLAVE_ID_INVALID) {
		if (sconfig->slave_id > TEGRA_APBDMA_CSR_REQ_SEL_MASK)
			return -EINVAL;
		else
			tdc->slave_id = sconfig->slave_id;
	}

Cheers
Jon