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    SubjectRe: [PATCH v7 3/5] misc: fuse: Add efuse driver for Tegra
    On Wed, Jun 11, 2014 at 05:58:28PM +0200, Stephen Warren wrote:
    > 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?
    >

    I'm not so sure about that. I have seen the hang when dumping all fuses using
    sysfs in an otherwise idle system booted from initrd. I don't think there
    should be any APB DMA activity going on then?

    Cheers,

    Peter.


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