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* [PATCH 0/1] Mediatek uart patch
@ 2021-07-10  9:01 Zhiyong Tao
  2021-07-10  9:01 ` [PATCH] uart: mediatek: fix memory corruption issue Zhiyong Tao
  0 siblings, 1 reply; 7+ messages in thread
From: Zhiyong Tao @ 2021-07-10  9:01 UTC (permalink / raw)
  To: timur, linux, alcooperx, tklauser, sean.wang
  Cc: srv_heupstream, zhiyong.tao, hui.liu, yuchen.huang, huihui.wang,
	eddie.huang, sean.wang, devicetree, linux-kernel,
	linux-arm-kernel, linux-mediatek, linux-serial

This series includes 1 patches:
1.fix uart access memory corruption issue

Zhiyong Tao (1):
  uart: mediatek: fix memory corruption issue

 drivers/tty/serial/8250/8250_mtk.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

--
2.18.0



^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH] uart: mediatek: fix memory corruption issue
  2021-07-10  9:01 [PATCH 0/1] Mediatek uart patch Zhiyong Tao
@ 2021-07-10  9:01 ` Zhiyong Tao
  2021-07-21 10:46   ` Greg KH
       [not found]   ` <CAHp75VeZL53VN0w3O160vMurmRT9ZJzJek6=4X6osqjJDuxD3g@mail.gmail.com>
  0 siblings, 2 replies; 7+ messages in thread
From: Zhiyong Tao @ 2021-07-10  9:01 UTC (permalink / raw)
  To: timur, linux, alcooperx, tklauser, sean.wang
  Cc: srv_heupstream, zhiyong.tao, hui.liu, yuchen.huang, huihui.wang,
	eddie.huang, sean.wang, devicetree, linux-kernel,
	linux-arm-kernel, linux-mediatek, linux-serial

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.
2. add processing mechanism which count value is 0

Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
---
 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) {
+		ptr = (unsigned char *)(data->rx_pos + dma->rx_buf);
+		copied = tty_insert_flip_string(tty_port, ptr, cnt);
+		data->rx_pos += cnt;
+	}
 
 	if (total > cnt) {
 		ptr = (unsigned char *)(dma->rx_buf);
@@ -120,6 +125,8 @@ static void mtk8250_dma_rx_complete(void *param)
 	tty_flip_buffer_push(tty_port);
 
 	mtk8250_rx_dma(up);
+
+	spin_unlock_irqrestore(&up->port.lock, flags);
 }
 
 static void mtk8250_rx_dma(struct uart_8250_port *up)
-- 
2.18.0


^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] uart: mediatek: fix memory corruption issue
  2021-07-10  9:01 ` [PATCH] uart: mediatek: fix memory corruption issue Zhiyong Tao
@ 2021-07-21 10:46   ` Greg KH
  2021-07-22 10:03     ` zhiyong tao
       [not found]   ` <CAHp75VeZL53VN0w3O160vMurmRT9ZJzJek6=4X6osqjJDuxD3g@mail.gmail.com>
  1 sibling, 1 reply; 7+ messages in thread
From: Greg KH @ 2021-07-21 10:46 UTC (permalink / raw)
  To: Zhiyong Tao
  Cc: timur, linux, alcooperx, tklauser, sean.wang, srv_heupstream,
	hui.liu, yuchen.huang, huihui.wang, eddie.huang, sean.wang,
	devicetree, linux-kernel, linux-arm-kernel, linux-mediatek,
	linux-serial

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.

> 2. add processing mechanism which count value is 0

What does this do?  And why is it needed?

> 
> Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>

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?

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"?

thanks,

greg k-h

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] uart: mediatek: fix memory corruption issue
       [not found]   ` <CAHp75VeZL53VN0w3O160vMurmRT9ZJzJek6=4X6osqjJDuxD3g@mail.gmail.com>
@ 2021-07-22  9:04     ` zhiyong tao
  0 siblings, 0 replies; 7+ messages in thread
From: zhiyong tao @ 2021-07-22  9:04 UTC (permalink / raw)
  To: Andy Shevchenko
  Cc: timur, linux, alcooperx, tklauser, sean.wang, srv_heupstream,
	hui.liu, yuchen.huang, huihui.wang, eddie.huang, sean.wang,
	devicetree, linux-kernel, linux-arm-kernel, linux-mediatek,
	linux-serial

On Wed, 2021-07-14 at 01:20 +0300, Andy Shevchenko wrote:
> 
> 
> On Saturday, July 10, 2021, Zhiyong Tao <zhiyong.tao@mediatek.com>
> wrote:
> 
> 
> Please, use “serial: 8260_mtk:” prefix.

==> Hi Andy,

Thanks for your suggestion.
we will change it in the next version.
> 
>         This patch is used to fix memory 
>         
> 
> 
> This is completely confusing start of the sentence. The form of “be
> used to” strongly suggests two things: 1) it was a patch to fix
> something; 2) it is not used anymore and never considered to be used
> again,
> 
> 
> Besides that Submitting Patches document highly recommends to avoid
> sentences that starts with “this patch”.
>  

==>We will change the commit message as "Fix uart corruption issue when
rx power off "in the next version.

Thanks.
>         
>         corruption issue when rx power off.
>         1. add spin lock in mtk8250_dma_rx_complete function in APDMA
>         mode.
>         2. add processing mechanism which count value is 0
>         
>         Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
>         ---
>          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) {
>         +               ptr = (unsigned char *)(data->rx_pos +
>         dma->rx_buf);
>         +               copied = tty_insert_flip_string(tty_port, ptr,
>         cnt);
>         +               data->rx_pos += cnt;
>         +       }
>         
>                 if (total > cnt) {
>                         ptr = (unsigned char *)(dma->rx_buf);
>         @@ -120,6 +125,8 @@ static void mtk8250_dma_rx_complete(void
>         *param)
>                 tty_flip_buffer_push(tty_port);
>         
>                 mtk8250_rx_dma(up);
>         +
>         +       spin_unlock_irqrestore(&up->port.lock, flags);
>          }
>         
>          static void mtk8250_rx_dma(struct uart_8250_port *up)
> 
> 

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] uart: mediatek: fix memory corruption issue
  2021-07-21 10:46   ` Greg KH
@ 2021-07-22 10:03     ` zhiyong tao
  2021-07-22 10:12       ` Greg KH
  0 siblings, 1 reply; 7+ messages in thread
From: zhiyong tao @ 2021-07-22 10:03 UTC (permalink / raw)
  To: Greg KH
  Cc: timur, linux, alcooperx, tklauser, sean.wang, srv_heupstream,
	hui.liu, zhiyong.tao, yuchen.huang, huihui.wang, eddie.huang,
	sean.wang, devicetree, linux-kernel, linux-arm-kernel,
	linux-mediatek, linux-serial

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".
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.
> 
> > 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.
> 
> > 
> > Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
> 
> 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.
> 
> 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.

Thanks.

> thanks,
> 
> greg k-h


^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] uart: mediatek: fix memory corruption issue
  2021-07-22 10:03     ` zhiyong tao
@ 2021-07-22 10:12       ` Greg KH
  2021-07-22 11:52         ` zhiyong tao
  0 siblings, 1 reply; 7+ messages in thread
From: Greg KH @ 2021-07-22 10:12 UTC (permalink / raw)
  To: zhiyong tao
  Cc: timur, linux, alcooperx, tklauser, sean.wang, srv_heupstream,
	hui.liu, yuchen.huang, huihui.wang, eddie.huang, sean.wang,
	devicetree, linux-kernel, linux-arm-kernel, linux-mediatek,
	linux-serial

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.

> > > 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?

> > > Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
> > 
> > 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?

> > 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.

thanks,

greg k-h

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] uart: mediatek: fix memory corruption issue
  2021-07-22 10:12       ` Greg KH
@ 2021-07-22 11:52         ` zhiyong tao
  0 siblings, 0 replies; 7+ messages in thread
From: zhiyong tao @ 2021-07-22 11:52 UTC (permalink / raw)
  To: Greg KH
  Cc: timur, linux, alcooperx, tklauser, sean.wang, srv_heupstream,
	hui.liu, yuchen.huang, huihui.wang, eddie.huang, sean.wang,
	devicetree, linux-kernel, linux-arm-kernel, linux-mediatek,
	linux-serial

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@mediatek.com>
> > > 
> > > 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


^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2021-07-22 11:53 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-07-10  9:01 [PATCH 0/1] Mediatek uart patch Zhiyong Tao
2021-07-10  9:01 ` [PATCH] uart: mediatek: fix memory corruption issue Zhiyong Tao
2021-07-21 10:46   ` Greg KH
2021-07-22 10:03     ` zhiyong tao
2021-07-22 10:12       ` Greg KH
2021-07-22 11:52         ` zhiyong tao
     [not found]   ` <CAHp75VeZL53VN0w3O160vMurmRT9ZJzJek6=4X6osqjJDuxD3g@mail.gmail.com>
2021-07-22  9:04     ` zhiyong tao

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