Re: Clock framework deadlock with external SPI clockchip
On Tue, Sep 03, 2013 at 04:22:29PM -0700, Mike Turquette wrote: > Quoting Lars-Peter Clausen (2013-08-30 06:24:45) > > === Clock chip driver ====== SPI master driver === > > clk_prepare_lock() > > spi_sync() > >wait_for_completion(X) > Is there a synchronous equivalent to spi_sync()? spi_sync() is synchronous? Obviously everything is asynchronous up to that point but the only way the driver can tell if the I/O completed is using spi_sync() or the equivalent thereof. If you're asking if there is a way of doing SPI I/O that isn't multi threaded then there isn't, in order to keep pushing transfers into the SPI controller to saturate the bus we have a high priority task to push more data in. SPI buses can be quite high bandwidth in some applications. signature.asc Description: Digital signature
Re: Clock framework deadlock with external SPI clockchip
On Tue, Sep 03, 2013 at 04:22:29PM -0700, Mike Turquette wrote: Quoting Lars-Peter Clausen (2013-08-30 06:24:45) === Clock chip driver ====== SPI master driver === clk_prepare_lock() spi_sync() wait_for_completion(X) Is there a synchronous equivalent to spi_sync()? spi_sync() is synchronous? Obviously everything is asynchronous up to that point but the only way the driver can tell if the I/O completed is using spi_sync() or the equivalent thereof. If you're asking if there is a way of doing SPI I/O that isn't multi threaded then there isn't, in order to keep pushing transfers into the SPI controller to saturate the bus we have a high priority task to push more data in. SPI buses can be quite high bandwidth in some applications. signature.asc Description: Digital signature
Re: Clock framework deadlock with external SPI clockchip
On 09/02/2013 01:18 PM, Peter De Schrijver wrote: > On Fri, Aug 30, 2013 at 03:24:45PM +0200, Lars-Peter Clausen wrote: >> Hi, >> >> I'm currently facing a deadlock in the common clock framework that >> unfortunately is not addressed by the reentrancy patches. I have a external >> clock chip that is controlled via SPI. So for example to configure the rate >> of the clock chip you need to send a SPI message. Naturally the clock >> framework will hold the prepare lock while configuring the rate. >> Communication in the SPI framework happens asynchronously, spi_sync() will >> enqueue a message in the SPI masters queue and then wait using >> wait_for_completion(). The master will call complete() once the transfer has >> been finished. The SPI master runs in it's own thread in which it processes >> the messages. In this thread it also calls clk_set_rate() to configure the >> SPI transfer clock rate based on what the message says. Now the deadlock >> happens as we try to take the prepare_lock again and since the clock chip >> and the SPI master run in different threads the reentrancy code does not >> kick in. >> >> The basic sequence is like this: >> >> === Clock chip driver ====== SPI master driver === >> clk_prepare_lock() >> spi_sync() >>wait_for_completion(X) >> clk_get_rate() >> clk_prepare_lock() <--- DEADLOCK >> clk_prepare_unlock() >> ... >> complete(X) >> ... >> clk_prepare_unlock() >> >> I'm wondering if you have any idea how this can be fixed. In my opinion we'd >> need a per clock mutex to address this properly. > > One workaround is to leave the SPI masters clock always prepared. A similar > problem can occur with I2C and DVFS using notifiers. That's kind of what I'm doing right now as a temporary solution. But we'd basically need to have all SPI or I2C master drivers to be aware that they might be used for controlling a external clock chip. And there are also situations where the workaround does not work. E.g. if the clk API is used to configure the rate of the SPI SCK signal, since the rate can be set by the spi message. - Lars -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Clock framework deadlock with external SPI clockchip
On Fri, Aug 30, 2013 at 03:24:45PM +0200, Lars-Peter Clausen wrote: > Hi, > > I'm currently facing a deadlock in the common clock framework that > unfortunately is not addressed by the reentrancy patches. I have a external > clock chip that is controlled via SPI. So for example to configure the rate > of the clock chip you need to send a SPI message. Naturally the clock > framework will hold the prepare lock while configuring the rate. > Communication in the SPI framework happens asynchronously, spi_sync() will > enqueue a message in the SPI masters queue and then wait using > wait_for_completion(). The master will call complete() once the transfer has > been finished. The SPI master runs in it's own thread in which it processes > the messages. In this thread it also calls clk_set_rate() to configure the > SPI transfer clock rate based on what the message says. Now the deadlock > happens as we try to take the prepare_lock again and since the clock chip > and the SPI master run in different threads the reentrancy code does not > kick in. > > The basic sequence is like this: > > === Clock chip driver ====== SPI master driver === > clk_prepare_lock() > spi_sync() >wait_for_completion(X) > clk_get_rate() > clk_prepare_lock() <--- DEADLOCK > clk_prepare_unlock() >... >complete(X) > ... > clk_prepare_unlock() > > I'm wondering if you have any idea how this can be fixed. In my opinion we'd > need a per clock mutex to address this properly. One workaround is to leave the SPI masters clock always prepared. A similar problem can occur with I2C and DVFS using notifiers. Cheers, Peter. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Clock framework deadlock with external SPI clockchip
On Fri, Aug 30, 2013 at 03:24:45PM +0200, Lars-Peter Clausen wrote: Hi, I'm currently facing a deadlock in the common clock framework that unfortunately is not addressed by the reentrancy patches. I have a external clock chip that is controlled via SPI. So for example to configure the rate of the clock chip you need to send a SPI message. Naturally the clock framework will hold the prepare lock while configuring the rate. Communication in the SPI framework happens asynchronously, spi_sync() will enqueue a message in the SPI masters queue and then wait using wait_for_completion(). The master will call complete() once the transfer has been finished. The SPI master runs in it's own thread in which it processes the messages. In this thread it also calls clk_set_rate() to configure the SPI transfer clock rate based on what the message says. Now the deadlock happens as we try to take the prepare_lock again and since the clock chip and the SPI master run in different threads the reentrancy code does not kick in. The basic sequence is like this: === Clock chip driver ====== SPI master driver === clk_prepare_lock() spi_sync() wait_for_completion(X) clk_get_rate() clk_prepare_lock() --- DEADLOCK clk_prepare_unlock() ... complete(X) ... clk_prepare_unlock() I'm wondering if you have any idea how this can be fixed. In my opinion we'd need a per clock mutex to address this properly. One workaround is to leave the SPI masters clock always prepared. A similar problem can occur with I2C and DVFS using notifiers. Cheers, Peter. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: Clock framework deadlock with external SPI clockchip
On 09/02/2013 01:18 PM, Peter De Schrijver wrote: On Fri, Aug 30, 2013 at 03:24:45PM +0200, Lars-Peter Clausen wrote: Hi, I'm currently facing a deadlock in the common clock framework that unfortunately is not addressed by the reentrancy patches. I have a external clock chip that is controlled via SPI. So for example to configure the rate of the clock chip you need to send a SPI message. Naturally the clock framework will hold the prepare lock while configuring the rate. Communication in the SPI framework happens asynchronously, spi_sync() will enqueue a message in the SPI masters queue and then wait using wait_for_completion(). The master will call complete() once the transfer has been finished. The SPI master runs in it's own thread in which it processes the messages. In this thread it also calls clk_set_rate() to configure the SPI transfer clock rate based on what the message says. Now the deadlock happens as we try to take the prepare_lock again and since the clock chip and the SPI master run in different threads the reentrancy code does not kick in. The basic sequence is like this: === Clock chip driver ====== SPI master driver === clk_prepare_lock() spi_sync() wait_for_completion(X) clk_get_rate() clk_prepare_lock() --- DEADLOCK clk_prepare_unlock() ... complete(X) ... clk_prepare_unlock() I'm wondering if you have any idea how this can be fixed. In my opinion we'd need a per clock mutex to address this properly. One workaround is to leave the SPI masters clock always prepared. A similar problem can occur with I2C and DVFS using notifiers. That's kind of what I'm doing right now as a temporary solution. But we'd basically need to have all SPI or I2C master drivers to be aware that they might be used for controlling a external clock chip. And there are also situations where the workaround does not work. E.g. if the clk API is used to configure the rate of the SPI SCK signal, since the rate can be set by the spi message. - Lars -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Clock framework deadlock with external SPI clockchip
Hi, I'm currently facing a deadlock in the common clock framework that unfortunately is not addressed by the reentrancy patches. I have a external clock chip that is controlled via SPI. So for example to configure the rate of the clock chip you need to send a SPI message. Naturally the clock framework will hold the prepare lock while configuring the rate. Communication in the SPI framework happens asynchronously, spi_sync() will enqueue a message in the SPI masters queue and then wait using wait_for_completion(). The master will call complete() once the transfer has been finished. The SPI master runs in it's own thread in which it processes the messages. In this thread it also calls clk_set_rate() to configure the SPI transfer clock rate based on what the message says. Now the deadlock happens as we try to take the prepare_lock again and since the clock chip and the SPI master run in different threads the reentrancy code does not kick in. The basic sequence is like this: === Clock chip driver ====== SPI master driver === clk_prepare_lock() spi_sync() wait_for_completion(X) clk_get_rate() clk_prepare_lock() <--- DEADLOCK clk_prepare_unlock() ... complete(X) ... clk_prepare_unlock() I'm wondering if you have any idea how this can be fixed. In my opinion we'd need a per clock mutex to address this properly. Thanks, - Lars -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Clock framework deadlock with external SPI clockchip
Hi, I'm currently facing a deadlock in the common clock framework that unfortunately is not addressed by the reentrancy patches. I have a external clock chip that is controlled via SPI. So for example to configure the rate of the clock chip you need to send a SPI message. Naturally the clock framework will hold the prepare lock while configuring the rate. Communication in the SPI framework happens asynchronously, spi_sync() will enqueue a message in the SPI masters queue and then wait using wait_for_completion(). The master will call complete() once the transfer has been finished. The SPI master runs in it's own thread in which it processes the messages. In this thread it also calls clk_set_rate() to configure the SPI transfer clock rate based on what the message says. Now the deadlock happens as we try to take the prepare_lock again and since the clock chip and the SPI master run in different threads the reentrancy code does not kick in. The basic sequence is like this: === Clock chip driver ====== SPI master driver === clk_prepare_lock() spi_sync() wait_for_completion(X) clk_get_rate() clk_prepare_lock() --- DEADLOCK clk_prepare_unlock() ... complete(X) ... clk_prepare_unlock() I'm wondering if you have any idea how this can be fixed. In my opinion we'd need a per clock mutex to address this properly. Thanks, - Lars -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
