Am 13.04.2013 19:04, schrieb Mauro Carvalho Chehab: > Em Sat, 13 Apr 2013 17:33:28 +0200 > Frank Schäfer <fschaefer.oss@xxxxxxxxxxxxxx> escreveu: > >> Am 13.04.2013 16:41, schrieb Mauro Carvalho Chehab: >>> Em Sat, 13 Apr 2013 11:48:39 +0200 >>> Frank Schäfer <fschaefer.oss@xxxxxxxxxxxxxx> escreveu: >>> >>>> The GPIO register tracking/caching code is partially broken, because newer >>>> devices provide more than one GPIO register and some of them are even using >>>> separate registers for read and write access. >>>> Making it work would be too complicated. >>>> It is also used nowhere and doesn't make sense in cases where input lines are >>>> connected to buttons etc. >>>> >>>> Signed-off-by: Frank Schäfer <fschaefer.oss@xxxxxxxxxxxxxx> >>>> --- >>>> drivers/media/usb/em28xx/em28xx-cards.c | 12 ------------ >>>> drivers/media/usb/em28xx/em28xx-core.c | 27 ++------------------------- >>>> drivers/media/usb/em28xx/em28xx.h | 6 ------ >>>> 3 Dateien geändert, 2 Zeilen hinzugefügt(+), 43 Zeilen entfernt(-) >>> ... >>> >>> >>>> @@ -231,14 +215,7 @@ int em28xx_write_reg_bits(struct em28xx *dev, u16 reg, u8 val, >>>> int oldval; >>>> u8 newval; >>>> >>>> - /* Uses cache for gpo/gpio registers */ >>>> - if (reg == dev->reg_gpo_num) >>>> - oldval = dev->reg_gpo; >>>> - else if (reg == dev->reg_gpio_num) >>>> - oldval = dev->reg_gpio; >>>> - else >>>> - oldval = em28xx_read_reg(dev, reg); >>>> - >>>> + oldval = em28xx_read_reg(dev, reg); >>>> if (oldval < 0) >>>> return oldval; >>> That's plain wrong, as it will break GPIO input. >>> >>> With GPIO, you can write either 0 or 1 to a GPIO output port. So, your >>> code works for output ports. >>> >>> However, an input port requires an specific value (either 1 or 0 depending >>> on the GPIO circuitry). If the wrong value is written there, the input port >>> will stop working. >>> >>> So, you can't simply read a value from a GPIO input and write it. You need >>> to shadow the GPIO write values instead. >> I don't understand what you mean. >> Why can I not read the value of a GPIO input and write it ? > Because, depending on the value you write, it can transform the input into an > output port. I don't get it. We always write to the GPIO register. That's why these functions are called em28xx_write_* ;) Whether the write operation is sane or not (e.g. because it modifies the bit corresponding to an input line) is not subject of these functions. Frank -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
