Re: [PATCH v7 3/5] misc: fuse: Add efuse driver for Tegra

Stephen Warren
2014-06-11T15:58:35Z

On 06/11/2014 09:25 AM, Peter De Schrijver wrote:
> On Wed, Jun 11, 2014 at 02:47:31PM +0200, Mikko Perttunen wrote:
>> On 05/06/14 16:09, Peter De Schrijver wrote:
>> ...
>>> +int tegra_fuse_readl(u32 offset, u32 *val)
>>> +{
>>> + if (!fuse_readl)
>>> + return -ENXIO;
>>> +
>>> + *val = fuse_readl(offset);
>>> +
>>> + return 0;
>>> +}
>>> +
>>
>> -EPROBE_DEFER would be a better error value, so that drivers can work
>
> Ok.
>
>> even if they are initially probed before the fuse driver. Of course, if
>> the fuse initialization is moved into machine init then this is a non-issue.
>
> The exported function will always be initialized later because on Tegra20 it
> requires APB DMA to be available. If you read the fuses directly, the system
> sometimes hangs.

That's not true in the current code. IIRC, the bug was that *if* an APB
DMA access to anything and a CPU access to the fuses happen at the same
time, then there can be a hang. As such, the current fuse code accesses
the fuses directly (without potential for a hang) if the APB DMA driver
is not available, but once the driver becomes available, it reads the
fuses through DMA instead. Does the new code not do that?