Serial: DaVinci: Revert double IIR test
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Quoted 6 lines · Philip Balister
Quoted 5 lines · Kevin Hilman
Quoted 2 lines · Mark Lokowich
Revert double IIR test in 8250 driver
Quoted 9 lines
Quoted 2 lines
Can you give a more detailed description of what the problem is that is being fixed?
Without this patch, serial console behavior is strange. You type and nothing is echoed and you hit return and things happen. It feels like two processes are grabbing input.
I think someone posted a more technical description, but I couldn't find it quickly.
Philip
This section of the driver is a test for faulty 16650 implementations that require a backup timer. The patch reverts the change that compares two states (instead of one, as in 2.6.25.2) of the IIR to determine if the workaround is required. The DaVinci UART does not need the backup timer, but the double conditional passed, enabling the timer and causing interrupt handling errors on the console and other UARTS.
Mark
Quoted 55 lines
Quoted 55 lines
This is in the generic 8250 driver so will affect all platforms. For this to be accepted, it should be discussed on linux-serial[1]
Kevin
Quoted 32 lines
Acked-by Jaswinder Singh <[email protected]>---
drivers/serial/8250.c +2
-3@@ -1867,7 +1867,6 @@ }if (is_real_interrupt (up->port.irq)) { -unsigned char iir1;/* * Test for UARTs that do not reassert THRE when the * transmitter is idle and the interrupt has already @@ -1881,7 +1880,7 @@wait_for_xmitr (up,UART_LSR_THRE );serial_out_sync (up,UART_IER ,UART_IER_THRI );udelay (1 );/* allow THRE to set */ - iir1 =serial_in (up,UART_IIR ); +serial_in (up,UART_IIR );serial_out (up,UART_IER ,0 );serial_out_sync (up,UART_IER ,UART_IER_THRI );udelay (1 );/* allow a working UART time to re-assert THRE */ @@ -1894,7 +1893,7 @@* If the interrupt is not reasserted, setup a timer to * kick the UART on a regular basis. */ -if (!(iir1 &UART_IIR_NO_INT ) && (iir &UART_IIR_NO_INT )) { +if (iir &UART_IIR_NO_INT ) {pr_debug ("ttyS%d - using backup timer\n" , port->line); up->timer.function = serial8250_backup_timeout; up->timer.data = (unsigned long )up;Quoted 4 lines
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Quoted 19 lines · Mark Lokowich
Quoted 9 lines · Philip Balister
Quoted 7 lines · Kevin Hilman
Quoted 2 lines · Mark Lokowich
Revert double IIR test in 8250 driver
Can you give a more detailed description of what the problem is that is being fixed?
Quoted 9 lines
Without this patch, serial console behavior is strange. You type and nothing is echoed and you hit return and things happen. It feels like two processes are grabbing input.
I think someone posted a more technical description, but I couldn't find it quickly.
Philip
Quoted 8 lines
This section of the driver is a test for faulty 16650 implementations that require a backup timer. The patch reverts the change that compares two states (instead of one, as in 2.6.25.2) of the IIR to determine if the workaround is required. The DaVinci UART does not need the backup timer, but the double conditional passed, enabling the timer and causing interrupt handling errors on the console and other UARTS.
Thanks Mark,
Do you have any recommendations for ways to conditionalize this code so the test still works on other platforms. Maybe via a new flag in platform data?
I want to be sure there is a mainline-acceptable fix here, so we are not divirging from mainline in generic code.
Kevin
Quoted 56 lines
Quoted 56 lines
Quoted 56 lines
This is in the generic 8250 driver so will affect all platforms. For this to be accepted, it should be discussed on linux-serial[1]
Kevin
Quoted 32 lines
Acked-by Jaswinder Singh <[email protected]>---
drivers/serial/8250.c +2
-3@@ -1867,7 +1867,6 @@ }if (is_real_interrupt (up->port.irq)) { -unsigned char iir1;/* * Test for UARTs that do not reassert THRE when the * transmitter is idle and the interrupt has already @@ -1881,7 +1880,7 @@wait_for_xmitr (up,UART_LSR_THRE );serial_out_sync (up,UART_IER ,UART_IER_THRI );udelay (1 );/* allow THRE to set */ - iir1 =serial_in (up,UART_IIR ); +serial_in (up,UART_IIR );serial_out (up,UART_IER ,0 );serial_out_sync (up,UART_IER ,UART_IER_THRI );udelay (1 );/* allow a working UART time to re-assert THRE */ @@ -1894,7 +1893,7 @@* If the interrupt is not reasserted, setup a timer to * kick the UART on a regular basis. */ -if (!(iir1 &UART_IIR_NO_INT ) && (iir &UART_IIR_NO_INT )) { +if (iir &UART_IIR_NO_INT ) {pr_debug ("ttyS%d - using backup timer\n" , port->line); up->timer.function = serial8250_backup_timeout; up->timer.data = (unsigned long )up;Quoted 4 lines
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