Messages in this thread | | | Date | Sat, 03 Dec 2005 22:19:58 +0300 | From | Vitaly Wool <> | Subject | Re: [spi-devel-general] Re: [PATCH 2.6-git] SPI core refresh |
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Mark Underwood wrote:
>--- vitalhome@rbcmail.ru wrote: > > > >>Mark, >> >> >> >>>>>I still do not see why you are stating this. Why do you say this? >>>>> >>>>> >>>>> >>>>> >>>>Due to possible priority inversion problems in David's core. >>>> >>>> >>>Which you still haven't proven, in fact you now seem to be changing your mind and saying >>>that >>>there might be a problem if an adapter driver was implemented badly although I still >>>don't see how >>>this could happen (the priority inversion I mean not the badly implemented driver ;). >>> >>> >>Truly admiring your deep understanding of the real-time technology, I should remind you >>that within the real-time conditions almost each event may happen and may not happen, for >>instance, two calls from different context to the same funtion may happen at the same or >>almost the same time, and may not happen that way. Therefore I used the word "possible". >>Hope I clarified that a bit for you. >> >>Please also see my previous emails for the explanation of how priority inversion can >>happen. This is not gonna be a rare case, BTW. >> >> > >Vitaly, > >First, please can you not change the CC list in the midle of a thread. > Yeah, sorry for that. You see, I was emailing not from my computer.
> >OK, looking through the code after a cup of coffe I can see the problem you are pointing out, >thank you :), for some reason I thought that that code was protected by a spin_lock :/. > >How to fix this? > >David, how would you feel about adding a NOT_DMAABLE flag in the spi_message structure? This >helper routine could then use this thus solving the one buffer to many callers problem (well >moving into the adapter driver, but as that serialise's transfers anyway I think this would remove >the priority inversion problem, Vitaly?) > >The other solution is to do a kmalloc for each caller (would could try to be smart and only do >that if the buffer is being used). > > And each one of the techniques suggested will make David's core closer to ours :)
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