On Thu, 2021-07-22 at 12:12 +0200, Greg KH wrote: > On Thu, Jul 22, 2021 at 06:03:32PM +0800, zhiyong tao wrote: > > On Wed, 2021-07-21 at 12:46 +0200, Greg KH wrote: > > > On Sat, Jul 10, 2021 at 05:01:03PM +0800, Zhiyong Tao wrote: > > > > This patch is used to fix memory corruption issue when rx power off. > > > > 1. add spin lock in mtk8250_dma_rx_complete function in APDMA mode. > > > > > > What does a lock protect from? Please be explicit and detailed. > > > > ==> Hi Gregkh, > > > > when uart is used as a communication port with external device(GPS). > > when external device(GPS) power off, the power of rx pin is also from > > 1.8v to 0v. Even if there is not any data in rx. But uart rx pin can > > capture the data "0". > > That sounds like a broken hardware design. > > > If uart don't receive any data in specified cycle, uart will generates > > BI(Break interrupt) interrupt. > > If external device(GPS) power off, we found that BI interrupt appeared > > continuously and very frequently. > > When uart interrupt type is BI, uart IRQ handler(8250 framwork > > API:serial8250_handle_irq) will push data to tty buffer. > > The code path: > > https://elixir.bootlin.com/linux/latest/source/drivers/tty/serial/8250/8250_port.c#L1917 > > > > mtk8250_dma_rx_complete is a task of mtk_uart_apdma_rx_handler. > > mtk8250_dma_rx_complete priority is lower than uart irq > > handler(serial8250_handle_irq). > > if we are in process of mtk8250_dma_rx_complete, uart appear BI > > interrupt:1)serial8250_handle_irq will priority execution.2)it may cause > > write tty buffer conflict in mtk8250_dma_rx_complete. > > So the spin lock protect the rx receive data process is not break. > > Then put something like this in the changelog text, as it is, it is not > descriptive at all. ==> Thanks for your suggestion. we will add it in changelog text([PATCH 0/1] Mediatek uart patch) in v1. > > > > > 2. add processing mechanism which count value is 0 > > > > > > What does this do? And why is it needed? > > > > ==> when count value is 0, we don't need push data to tty buffer. > > so we add it. > > But that does not actually do anything different from what it does > today. And it has nothing to do with the lock, so this should be 2 > different patches, right? ==> yes, it has nothing to do with the lock. we will separate it in v1. > > > > > Signed-off-by: Zhiyong Tao <zhiyong.tao@xxxxxxxxxxxx> > > > > > > What commit does this fix? Does this need to go to stable kernel trees? > > > If so, how far back? > > > > > > > --- > > > > drivers/tty/serial/8250/8250_mtk.c | 15 +++++++++++---- > > > > 1 file changed, 11 insertions(+), 4 deletions(-) > > > > > > > > diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c > > > > index f7d3023f860f..09f7d2166315 100644 > > > > --- a/drivers/tty/serial/8250/8250_mtk.c > > > > +++ b/drivers/tty/serial/8250/8250_mtk.c > > > > @@ -91,12 +91,15 @@ static void mtk8250_dma_rx_complete(void *param) > > > > struct mtk8250_data *data = up->port.private_data; > > > > struct tty_port *tty_port = &up->port.state->port; > > > > struct dma_tx_state state; > > > > - int copied, total, cnt; > > > > + unsigned int copied, total, cnt; > > > > unsigned char *ptr; > > > > + unsigned long flags; > > > > > > > > if (data->rx_status == DMA_RX_SHUTDOWN) > > > > return; > > > > > > > > + spin_lock_irqsave(&up->port.lock, flags); > > > > + > > > > dmaengine_tx_status(dma->rxchan, dma->rx_cookie, &state); > > > > total = dma->rx_size - state.residue; > > > > cnt = total; > > > > @@ -104,9 +107,11 @@ static void mtk8250_dma_rx_complete(void *param) > > > > if ((data->rx_pos + cnt) > dma->rx_size) > > > > cnt = dma->rx_size - data->rx_pos; > > > > > > > > - ptr = (unsigned char *)(data->rx_pos + dma->rx_buf); > > > > - copied = tty_insert_flip_string(tty_port, ptr, cnt); > > > > - data->rx_pos += cnt; > > > > + if (cnt != 0) { > > > > > > Why does cnt matter here? If cnt is 0, the code above should not do > > > anything at all, right? > > > > ==> yes, if the counter value is 0, we don't need push data to the tty > > buffer. > > But this does not change the logic as if cnt is 0, nothing gets pushed > with the current code either, right? ==> yes, it is. > > > > Or if it does, should we change tty_insert_flip_string() to always check > > > for cnt != 0 before it does the first loop? Hm, it looks like it will > > > abort if cnt is 0, so what is this change really doing? Why do you need > > > it? What is it "fixing"? > > > > > ==> It is not fix anything, we just think if count value is 0, we don't > > need do anything. > > Then make it a separate patch, independant from the lock patch, and we > can discuss it there. Do NOT have patches do multiple things. ==> I will make it a separate patch in v1. Thanks. > > thanks, > > greg k-h