linux-kernel - Re: [PATCH] dw_dmac: don't exceed AHB master number in dwc_get_data

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Date:	Tue, 15 Jan 2013 09:05:38 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Vinod Koul <vinod.koul@...el.com>,
	linux-kernel@...r.kernel.org, spear-devel <spear-devel@...t.st.com>
Subject: Re: [PATCH] dw_dmac: don't exceed AHB master number in dwc_get_data_width

On Tue, Jan 15, 2013 at 3:54 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On Mon, Jan 14, 2013 at 7:50 PM, Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
>> The driver's default assumes that hardware has two AHB masters which might be
>> not true. In such rare cases we have not to exceed a number of the AHB masters
>> present in the hardware. Thus, the AHB master with highest possible number will
>> be used to retrieve the data witdh value.
>>
>> The patch also changes the logic a bit when the master parameter of the
>> dwc_get_data_width() is out of range. Now the function will return a value
>> related to the first AHB master.
>>
>> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>> ---
>>  drivers/dma/dw_dmac.c |    7 ++++---
>>  1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
>> index 30ff2a4..b2d564a 100644
>> --- a/drivers/dma/dw_dmac.c
>> +++ b/drivers/dma/dw_dmac.c
>> @@ -80,13 +80,14 @@ static inline unsigned int dwc_get_data_width(struct dma_chan *chan, int master)
>>  {
>>         struct dw_dma *dw = to_dw_dma(chan->device);
>>         struct dw_dma_slave *dws = chan->private;
>> +       unsigned int m = 0;
>>
>>         if (master == SRC_MASTER)
>> -               return dw->data_width[dwc_get_sms(dws)];
>> +               m = dwc_get_sms(dws);
>>         else if (master == DST_MASTER)
>> -               return dw->data_width[dwc_get_dms(dws)];
>> +               m = dwc_get_dms(dws);
>>
>> -       return 0;
>> +       return dw->data_width[min_t(unsigned int, dw->nr_masters - 1, m)];
>
> The details of the patch are fine, but i didn't get how do you get
> master 1 selected
> on a system where you have only 1 master?

min_t(..., nr_masters - 1, m) defines this. m is returned value with
default settings, let's say 1. In that case if nr_masters is also 1
the min_t(..., 1-1, 1) returns 0.

The value of nr_masters itself is come from autoconfig or platform data.

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-- 
With Best Regards,
Andy Shevchenko
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