[PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Bin Meng]

GCC seems to be strict about processing pattern like "!!for & bar".
When 'bar' is not 0 or 1, it complains with -Werror=parentheses:

  suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]

Add a () around "foo && bar", which also improves code readability.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
---

 hw/dma/sifive_pdma.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
index b4fd40573a..b8ec7621f3 100644
--- a/hw/dma/sifive_pdma.c
+++ b/hw/dma/sifive_pdma.c
@@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
     offset &= 0xfff;
     switch (offset) {
     case DMA_CONTROL:
-        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
+        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
 
         if (!claimed && (value & CONTROL_CLAIM)) {
             /* reset Next* registers */
-- 
2.25.1

[PATCH 2/2] hw/dma: sifive_pdma: Don't run DMA when channel is disclaimed

[Bin Meng]

If Control.run bit is set while not preserving the Control.claim
bit, the DMA transfer shall not be started.

The following result is PDMA tested in U-Boot on Unleashed board:

=> mw.l 0x3000000 0x0                      <= Disclaim channel 0
=> mw.l 0x3000000 0x1                      <= Claim channel 0
=> mw.l 0x3000004 0x55000000               <= wsize = rsize = 5 (2^5 = 32 bytes)
=> mw.q 0x3000008 0x2                      <= NextBytes = 2
=> mw.q 0x3000010 0x84000000               <= NextDestination = 0x84000000
=> mw.q 0x3000018 0x84001000               <= NextSource = 0x84001000
=> mw.l 0x84000000 0x87654321              <= Fill test data to dst
=> mw.l 0x84001000 0x12345678              <= Fill test data to src
=> md.l 0x84000000 1; md.l 0x84001000 1    <= Dump src/dst memory contents
84000000: 87654321                               !Ce.
84001000: 12345678                               xV4.
=> md.l 0x3000000 8                        <= Dump PDMA status
03000000: 00000001 55000000 00000002 00000000    .......U........
03000010: 84000000 00000000 84001000 00000000    ................
=> mw.l 0x3000000 0x2                      <= Set channel 0 run bit only
=> md.l 0x3000000 8                        <= Dump PDMA status
03000000: 00000000 55000000 00000002 00000000    .......U........
03000010: 84000000 00000000 84001000 00000000    ................
=> md.l 0x84000000 1; md.l 0x84001000 1    <= Dump src/dst memory contents
84000000: 87654321                               !Ce.
84001000: 12345678                               xV4.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
---

 hw/dma/sifive_pdma.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
index b8ec7621f3..85fe34f5f3 100644
--- a/hw/dma/sifive_pdma.c
+++ b/hw/dma/sifive_pdma.c
@@ -232,7 +232,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
 {
     SiFivePDMAState *s = opaque;
     int ch = SIFIVE_PDMA_CHAN_NO(offset);
-    bool claimed;
+    bool claimed, run;
 
     if (ch >= SIFIVE_PDMA_CHANS) {
         qemu_log_mask(LOG_GUEST_ERROR, "%s: Invalid channel no %d\n",
@@ -244,6 +244,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
     switch (offset) {
     case DMA_CONTROL:
         claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
+        run = !!(s->chan[ch].control & CONTROL_RUN);
 
         if (!claimed && (value & CONTROL_CLAIM)) {
             /* reset Next* registers */
@@ -254,13 +255,19 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
             s->chan[ch].next_src = 0;
         }
 
+        /* claim bit can only be cleared when run is low */
+        if (run && !(value & CONTROL_CLAIM)) {
+            value |= CONTROL_CLAIM;
+        }
+
         s->chan[ch].control = value;
 
         /*
          * If channel was not claimed before run bit is set,
+         * or if the channel is disclaimed when run was low,
          * DMA won't run.
          */
-        if (!claimed) {
+        if (!claimed || (!run && !(value & CONTROL_CLAIM))) {
             s->chan[ch].control &= ~CONTROL_RUN;
             return;
         }
-- 
2.25.1

Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Philippe Mathieu-Daudé]

On 9/27/21 04:21, Bin Meng wrote:
> GCC seems to be strict about processing pattern like "!!for & bar".
> When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
> 
>   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]
> 
> Add a () around "foo && bar", which also improves code readability.
> 
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> ---
> 
>  hw/dma/sifive_pdma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
> index b4fd40573a..b8ec7621f3 100644
> --- a/hw/dma/sifive_pdma.c
> +++ b/hw/dma/sifive_pdma.c
> @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
>      offset &= 0xfff;
>      switch (offset) {
>      case DMA_CONTROL:
> -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
> +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);

AFAIK in C logical NOT has precedence over bitwise AND, so IIUC
compilers should read the current code as:

           claimed (!!s->chan[ch].control) & CONTROL_CLAIM;

meaning this patch is doing more than "improve code readability",
this is a logical change and likely a bug fix...

BTW GCC suggestions are:

           claimed (!!s->chan[ch].control) & CONTROL_CLAIM;

           claimed (!!s->chan[ch].control) && CONTROL_CLAIM;
>  
>          if (!claimed && (value & CONTROL_CLAIM)) {
>              /* reset Next* registers */
> 

Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Philippe Mathieu-Daudé]

On 9/27/21 06:47, Philippe Mathieu-Daudé wrote:
> On 9/27/21 04:21, Bin Meng wrote:
>> GCC seems to be strict about processing pattern like "!!for & bar".

What GCC version btw?

>> When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
>>
>>   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]
>>
>> Add a () around "foo && bar", which also improves code readability.
>>
>> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
>> ---
>>
>>  hw/dma/sifive_pdma.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
>> index b4fd40573a..b8ec7621f3 100644
>> --- a/hw/dma/sifive_pdma.c
>> +++ b/hw/dma/sifive_pdma.c
>> @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
>>      offset &= 0xfff;
>>      switch (offset) {
>>      case DMA_CONTROL:
>> -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
>> +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
> 
> AFAIK in C logical NOT has precedence over bitwise AND, so IIUC
> compilers should read the current code as:
> 
>            claimed (!!s->chan[ch].control) & CONTROL_CLAIM;
> 
> meaning this patch is doing more than "improve code readability",
> this is a logical change and likely a bug fix...
> 
> BTW GCC suggestions are:
> 
>            claimed (!!s->chan[ch].control) & CONTROL_CLAIM;
> 
>            claimed (!!s->chan[ch].control) && CONTROL_CLAIM;
>>  
>>          if (!claimed && (value & CONTROL_CLAIM)) {
>>              /* reset Next* registers */
>>
> 
> 

Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Bin Meng]

Hi Philippe,

On Mon, Sep 27, 2021 at 12:47 PM Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> On 9/27/21 04:21, Bin Meng wrote:
> > GCC seems to be strict about processing pattern like "!!for & bar".
> > When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
> >
> >   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]
> >
> > Add a () around "foo && bar", which also improves code readability.
> >
> > Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> > ---
> >
> >  hw/dma/sifive_pdma.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
> > index b4fd40573a..b8ec7621f3 100644
> > --- a/hw/dma/sifive_pdma.c
> > +++ b/hw/dma/sifive_pdma.c
> > @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
> >      offset &= 0xfff;
> >      switch (offset) {
> >      case DMA_CONTROL:
> > -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
> > +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
>
> AFAIK in C logical NOT has precedence over bitwise AND, so IIUC
> compilers should read the current code as:
>
>            claimed (!!s->chan[ch].control) & CONTROL_CLAIM;
>
> meaning this patch is doing more than "improve code readability",
> this is a logical change and likely a bug fix...

Yes, you are correct. Indeed this is a bug fix. I did not dig into the
operator precedence in detail. I will reword this in v2.

>
> BTW GCC suggestions are:
>
>            claimed (!!s->chan[ch].control) & CONTROL_CLAIM;
>
>            claimed (!!s->chan[ch].control) && CONTROL_CLAIM;
> >
> >          if (!claimed && (value & CONTROL_CLAIM)) {
> >              /* reset Next* registers */
> >

I was using GCC 9.3.0 on Ubuntu 20.04.

Regards,
Bin

Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Bin Meng]

Hi Philippe,

On Mon, Sep 27, 2021 at 12:47 PM Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> On 9/27/21 04:21, Bin Meng wrote:
> > GCC seems to be strict about processing pattern like "!!for & bar".
> > When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
> >
> >   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]
> >
> > Add a () around "foo && bar", which also improves code readability.
> >
> > Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> > ---
> >
> >  hw/dma/sifive_pdma.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
> > index b4fd40573a..b8ec7621f3 100644
> > --- a/hw/dma/sifive_pdma.c
> > +++ b/hw/dma/sifive_pdma.c
> > @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
> >      offset &= 0xfff;
> >      switch (offset) {
> >      case DMA_CONTROL:
> > -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
> > +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
>
> AFAIK in C logical NOT has precedence over bitwise AND, so IIUC
> compilers should read the current code as:
>
>            claimed (!!s->chan[ch].control) & CONTROL_CLAIM;
>
> meaning this patch is doing more than "improve code readability",
> this is a logical change and likely a bug fix...

Yes, you are correct. Indeed this is a bug fix. I did not dig into the
operator precedence in detail. I will reword this in v2.

>
> BTW GCC suggestions are:
>
>            claimed (!!s->chan[ch].control) & CONTROL_CLAIM;
>
>            claimed (!!s->chan[ch].control) && CONTROL_CLAIM;
> >
> >          if (!claimed && (value & CONTROL_CLAIM)) {
> >              /* reset Next* registers */
> >

I was using GCC 9.3.0 on Ubuntu 20.04.

Regards,
Bin

Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Markus Armbruster]

Bin Meng <bmeng.cn@gmail.com> writes:

> GCC seems to be strict about processing pattern like "!!for & bar".
> When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
>
>   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]
>
> Add a () around "foo && bar", which also improves code readability.
>
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> ---
>
>  hw/dma/sifive_pdma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
> index b4fd40573a..b8ec7621f3 100644
> --- a/hw/dma/sifive_pdma.c
> +++ b/hw/dma/sifive_pdma.c
> @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
>      offset &= 0xfff;
>      switch (offset) {
>      case DMA_CONTROL:
> -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
> +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
>  
>          if (!claimed && (value & CONTROL_CLAIM)) {
>              /* reset Next* registers */

Old code

    first double-negate, mapping zero to zero, non-zero to one
    then mask, which does nothing, because CONTROL_CLAIM is 1

New code:

    first mask, yielding 0 or 1
    then double-negate, which does nothing

Looks like a bug fix to me.  If I'm right, the commit message is wrong,
and the double negate is redundant.

Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Markus Armbruster]

Bin Meng <bmeng.cn@gmail.com> writes:

> GCC seems to be strict about processing pattern like "!!for & bar".
> When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
>
>   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]
>
> Add a () around "foo && bar", which also improves code readability.
>
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> ---
>
>  hw/dma/sifive_pdma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
> index b4fd40573a..b8ec7621f3 100644
> --- a/hw/dma/sifive_pdma.c
> +++ b/hw/dma/sifive_pdma.c
> @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
>      offset &= 0xfff;
>      switch (offset) {
>      case DMA_CONTROL:
> -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
> +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
>  
>          if (!claimed && (value & CONTROL_CLAIM)) {
>              /* reset Next* registers */

Old code

    first double-negate, mapping zero to zero, non-zero to one
    then mask, which does nothing, because CONTROL_CLAIM is 1

New code:

    first mask, yielding 0 or 1
    then double-negate, which does nothing

Looks like a bug fix to me.  If I'm right, the commit message is wrong,
and the double negate is redundant.

Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Bin Meng]

Hi Markus,

On Mon, Sep 27, 2021 at 2:51 PM Markus Armbruster <armbru@redhat.com> wrote:
>
> Bin Meng <bmeng.cn@gmail.com> writes:
>
> > GCC seems to be strict about processing pattern like "!!for & bar".
> > When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
> >
> >   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]
> >
> > Add a () around "foo && bar", which also improves code readability.
> >
> > Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> > ---
> >
> >  hw/dma/sifive_pdma.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
> > index b4fd40573a..b8ec7621f3 100644
> > --- a/hw/dma/sifive_pdma.c
> > +++ b/hw/dma/sifive_pdma.c
> > @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
> >      offset &= 0xfff;
> >      switch (offset) {
> >      case DMA_CONTROL:
> > -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
> > +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
> >
> >          if (!claimed && (value & CONTROL_CLAIM)) {
> >              /* reset Next* registers */
>
> Old code
>
>     first double-negate, mapping zero to zero, non-zero to one
>     then mask, which does nothing, because CONTROL_CLAIM is 1
>
> New code:
>
>     first mask, yielding 0 or 1
>     then double-negate, which does nothing
>
> Looks like a bug fix to me.  If I'm right, the commit message is wrong,
> and the double negate is redundant.
>

Thanks for the review. The double negate is not needed with
CONTROL_CLAIM which is 1, but is needed if the bit is in another
position.

Regards,
Bin

Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Bin Meng]

Hi Markus,

On Mon, Sep 27, 2021 at 2:51 PM Markus Armbruster <armbru@redhat.com> wrote:
>
> Bin Meng <bmeng.cn@gmail.com> writes:
>
> > GCC seems to be strict about processing pattern like "!!for & bar".
> > When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
> >
> >   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]
> >
> > Add a () around "foo && bar", which also improves code readability.
> >
> > Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> > ---
> >
> >  hw/dma/sifive_pdma.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
> > index b4fd40573a..b8ec7621f3 100644
> > --- a/hw/dma/sifive_pdma.c
> > +++ b/hw/dma/sifive_pdma.c
> > @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
> >      offset &= 0xfff;
> >      switch (offset) {
> >      case DMA_CONTROL:
> > -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
> > +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
> >
> >          if (!claimed && (value & CONTROL_CLAIM)) {
> >              /* reset Next* registers */
>
> Old code
>
>     first double-negate, mapping zero to zero, non-zero to one
>     then mask, which does nothing, because CONTROL_CLAIM is 1
>
> New code:
>
>     first mask, yielding 0 or 1
>     then double-negate, which does nothing
>
> Looks like a bug fix to me.  If I'm right, the commit message is wrong,
> and the double negate is redundant.
>

Thanks for the review. The double negate is not needed with
CONTROL_CLAIM which is 1, but is needed if the bit is in another
position.

Regards,
Bin

Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Markus Armbruster]

Bin Meng <bmeng.cn@gmail.com> writes:

> Hi Markus,
>
> On Mon, Sep 27, 2021 at 2:51 PM Markus Armbruster <armbru@redhat.com> wrote:
>>
>> Bin Meng <bmeng.cn@gmail.com> writes:
>>
>> > GCC seems to be strict about processing pattern like "!!for & bar".
>> > When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
>> >
>> >   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]
>> >
>> > Add a () around "foo && bar", which also improves code readability.
>> >
>> > Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
>> > ---
>> >
>> >  hw/dma/sifive_pdma.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
>> > index b4fd40573a..b8ec7621f3 100644
>> > --- a/hw/dma/sifive_pdma.c
>> > +++ b/hw/dma/sifive_pdma.c
>> > @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
>> >      offset &= 0xfff;
>> >      switch (offset) {
>> >      case DMA_CONTROL:
>> > -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
>> > +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
>> >
>> >          if (!claimed && (value & CONTROL_CLAIM)) {
>> >              /* reset Next* registers */
>>
>> Old code
>>
>>     first double-negate, mapping zero to zero, non-zero to one
>>     then mask, which does nothing, because CONTROL_CLAIM is 1
>>
>> New code:
>>
>>     first mask, yielding 0 or 1
>>     then double-negate, which does nothing
>>
>> Looks like a bug fix to me.  If I'm right, the commit message is wrong,
>> and the double negate is redundant.
>>
>
> Thanks for the review. The double negate is not needed with
> CONTROL_CLAIM which is 1, but is needed if the bit is in another
> position.

It's not needed even then: conversion from integer type to bool takes
care of it.  It's not wrong, though.

However, the commit message does look wrong to me.

Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Markus Armbruster]

Bin Meng <bmeng.cn@gmail.com> writes:

> Hi Markus,
>
> On Mon, Sep 27, 2021 at 2:51 PM Markus Armbruster <armbru@redhat.com> wrote:
>>
>> Bin Meng <bmeng.cn@gmail.com> writes:
>>
>> > GCC seems to be strict about processing pattern like "!!for & bar".
>> > When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
>> >
>> >   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Werror=parentheses]
>> >
>> > Add a () around "foo && bar", which also improves code readability.
>> >
>> > Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
>> > ---
>> >
>> >  hw/dma/sifive_pdma.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
>> > index b4fd40573a..b8ec7621f3 100644
>> > --- a/hw/dma/sifive_pdma.c
>> > +++ b/hw/dma/sifive_pdma.c
>> > @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
>> >      offset &= 0xfff;
>> >      switch (offset) {
>> >      case DMA_CONTROL:
>> > -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
>> > +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
>> >
>> >          if (!claimed && (value & CONTROL_CLAIM)) {
>> >              /* reset Next* registers */
>>
>> Old code
>>
>>     first double-negate, mapping zero to zero, non-zero to one
>>     then mask, which does nothing, because CONTROL_CLAIM is 1
>>
>> New code:
>>
>>     first mask, yielding 0 or 1
>>     then double-negate, which does nothing
>>
>> Looks like a bug fix to me.  If I'm right, the commit message is wrong,
>> and the double negate is redundant.
>>
>
> Thanks for the review. The double negate is not needed with
> CONTROL_CLAIM which is 1, but is needed if the bit is in another
> position.

It's not needed even then: conversion from integer type to bool takes
care of it.  It's not wrong, though.

However, the commit message does look wrong to me.