Messages in this thread | | | Date | Mon, 14 Jun 2010 22:20:30 +0200 | From | Yury Georgievskiy <> | Subject | Re: [PATCH 1/1] serial: mcf: Don't take spinlocks in already protected functions |
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Andrew Morton wrote: > On Wed, 9 Jun 2010 09:56:26 +0200 > ygeorgie@gmail.com wrote: > > > From: Yury Georgievskiy <ygeorgie@gmail.com> > > > > Don't take the port spinlock in uart functions where the serial core > > already takes care of locking/unlocking them. > > > > The code would actually lock up on architectures where spinlocks are > > implemented. > > > > Also protect calling mcf_rx_chars/mcf_tx_chars in the > > interrupt handler by the port spinlock and use IRQ_RETVAL > > to return from isr. > > > > Thanks. Did you runtime test this?
Unfortunately not.
I spotted it as I am now writing the UART driver for Philips SCC2698B integrated circuit and was looking for serial drivers examples.
And also came across d8d721f4c005f9a69bd1b5d5c6ba99b7e1d464de commit that has patched a similar problem.
> > > @@ -368,11 +354,15 @@ static irqreturn_t mcf_interrupt(int irq, void *data) > > unsigned int isr; > > > > isr = readb(port->membase + MCFUART_UISR) & pp->imr; > > + > > + spin_lock(&port->lock); > > if (isr & MCFUART_UIR_RXREADY) > > mcf_rx_chars(pp); > > if (isr & MCFUART_UIR_TXREADY) > > mcf_tx_chars(pp); > > - return IRQ_HANDLED; > > + spin_unlock(&port->lock); > > + > > + return IRQ_RETVAL(isr); > > } > > I think this is a little abusive of IRQ_RETVAL. If there are some bits > set in `isr' other than MCFUART_UIR_RXREADY and MCFUART_UIR_TXREADY, we > claim we handled it, only we didn't. > > Probably the code works OK, but it all seems a bit uncomfortable. > Perhaps make it more explicit? >
Fair enough. The code looks more relevant.
> > --- a/drivers/serial/mcf.c~serial-mcf-dont-take-spinlocks-in-already-protected-functions-fix > +++ a/drivers/serial/mcf.c > @@ -352,17 +352,22 @@ static irqreturn_t mcf_interrupt(int irq > struct uart_port *port = data; > struct mcf_uart *pp = container_of(port, struct mcf_uart, port); > unsigned int isr; > + irqreturn_t ret = IRQ_NONE; > > isr = readb(port->membase + MCFUART_UISR) & pp->imr; > > spin_lock(&port->lock); > - if (isr & MCFUART_UIR_RXREADY) > + if (isr & MCFUART_UIR_RXREADY) { > mcf_rx_chars(pp); > - if (isr & MCFUART_UIR_TXREADY) > + ret = IRQ_HANDLED; > + } > + if (isr & MCFUART_UIR_TXREADY) { > mcf_tx_chars(pp); > + ret = IRQ_HANDLED; > + } > spin_unlock(&port->lock); > > - return IRQ_RETVAL(isr); > + return ret; > } > > /****************************************************************************/ > _ >
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