Re: [PATCH] xhci: Use ffs() to find page size in xhci_mem_init()

[Andrey Smirnov]

On Thu, Feb 7, 2019 at 1:00 AM Mathias Nyman
 wrote:
>
> On 07.02.2019 02:03, Andrey Smirnov wrote:
> > Get page size order using ffs() instead of open coding it with a loop.
> >
> > Signed-off-by: Andrey Smirnov 
> > Cc: Mathias Nyman 
> > Cc: Greg Kroah-Hartman 
> > Cc: linux-...@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > ---
> >   drivers/usb/host/xhci-mem.c | 6 +-
> >   1 file changed, 1 insertion(+), 5 deletions(-)
> >
> > diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> > index 36a3eb8849f1..44b43c3d819f 100644
> > --- a/drivers/usb/host/xhci-mem.c
> > +++ b/drivers/usb/host/xhci-mem.c
> > @@ -2362,11 +2362,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
> >   page_size = readl(>op_regs->page_size);
> >   xhci_dbg_trace(xhci, trace_xhci_dbg_init,
> >   "Supported page size register = 0x%x", page_size);
> > - for (i = 0; i < 16; i++) {
> > - if ((0x1 & page_size) != 0)
> > - break;
> > - page_size = page_size >> 1;
> > - }
> > + i = ffs(page_size);
> >   if (i < 16)
> >   xhci_dbg_trace(xhci, trace_xhci_dbg_init,
> >   "Supported page size of %iK", (1 << (i+12)) / 1024);
>
> Hi
>
> using ffs() is a welcome change, but it will give different a result than the 
> loop.
>
> *old loop
>valid page_size value if i < 16
> *ffs()
>valid page_size value if i >= 1 and i < 17
>

My bad, sorry about that, was using __fls() in the version I tested,
but then switched it to ffs() at the last minute and forgot to double
check. Will update in v2.

Thanks,
Andrey Smirnov

Re: [PATCH] xhci: Use ffs() to find page size in xhci_mem_init()

[Mathias Nyman]

On 07.02.2019 12:58, Felipe Balbi wrote:


Hi,

Mathias Nyman  writes:

Get page size order using ffs() instead of open coding it with a loop.

Signed-off-by: Andrey Smirnov 
Cc: Mathias Nyman 
Cc: Greg Kroah-Hartman 
Cc: linux-...@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
drivers/usb/host/xhci-mem.c | 6 +-
1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 36a3eb8849f1..44b43c3d819f 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -2362,11 +2362,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
page_size = readl(>op_regs->page_size);
xhci_dbg_trace(xhci, trace_xhci_dbg_init,
"Supported page size register = 0x%x", page_size);
-   for (i = 0; i < 16; i++) {
-   if ((0x1 & page_size) != 0)
-   break;
-   page_size = page_size >> 1;
-   }
+   i = ffs(page_size);
if (i < 16)
xhci_dbg_trace(xhci, trace_xhci_dbg_init,
"Supported page size of %iK", (1 << (i+12)) / 1024);


Hi

using ffs() is a welcome change, but it will give different a result than the 
loop.

*old loop
 valid page_size value if i < 16
*ffs()
 valid page_size value if i >= 1 and i < 17


off-by-one, just use i = ffs() - 1. Or use __ffs().


and handle the page_size == 0 case.


Can it be zero in real life, or are you protecting against academic
possibility that's never going to happen in HW?



whole page_size check is not really doing much, just printing out
different debug messages.

-Mathias

Re: [PATCH] xhci: Use ffs() to find page size in xhci_mem_init()

[Felipe Balbi]

Hi,

Mathias Nyman  writes:
 Get page size order using ffs() instead of open coding it with a loop.

 Signed-off-by: Andrey Smirnov 
 Cc: Mathias Nyman 
 Cc: Greg Kroah-Hartman 
 Cc: linux-...@vger.kernel.org
 Cc: linux-kernel@vger.kernel.org
 ---
drivers/usb/host/xhci-mem.c | 6 +-
1 file changed, 1 insertion(+), 5 deletions(-)

 diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
 index 36a3eb8849f1..44b43c3d819f 100644
 --- a/drivers/usb/host/xhci-mem.c
 +++ b/drivers/usb/host/xhci-mem.c
 @@ -2362,11 +2362,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t 
 flags)
page_size = readl(>op_regs->page_size);
xhci_dbg_trace(xhci, trace_xhci_dbg_init,
"Supported page size register = 0x%x", 
 page_size);
 -  for (i = 0; i < 16; i++) {
 -  if ((0x1 & page_size) != 0)
 -  break;
 -  page_size = page_size >> 1;
 -  }
 +  i = ffs(page_size);
if (i < 16)
xhci_dbg_trace(xhci, trace_xhci_dbg_init,
"Supported page size of %iK", (1 << (i+12)) / 
 1024);
>>>
>>> Hi
>>>
>>> using ffs() is a welcome change, but it will give different a result than 
>>> the loop.
>>>
>>> *old loop
>>> valid page_size value if i < 16
>>> *ffs()
>>> valid page_size value if i >= 1 and i < 17
>> 
>> off-by-one, just use i = ffs() - 1. Or use __ffs().
>
> and handle the page_size == 0 case.

Can it be zero in real life, or are you protecting against academic
possibility that's never going to happen in HW?

-- 
balbi


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Re: [PATCH] xhci: Use ffs() to find page size in xhci_mem_init()

[Mathias Nyman]

On 07.02.2019 11:06, Felipe Balbi wrote:


Hi,

Mathias Nyman  writes:

On 07.02.2019 02:03, Andrey Smirnov wrote:

Get page size order using ffs() instead of open coding it with a loop.

Signed-off-by: Andrey Smirnov 
Cc: Mathias Nyman 
Cc: Greg Kroah-Hartman 
Cc: linux-...@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
   drivers/usb/host/xhci-mem.c | 6 +-
   1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 36a3eb8849f1..44b43c3d819f 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -2362,11 +2362,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
page_size = readl(>op_regs->page_size);
xhci_dbg_trace(xhci, trace_xhci_dbg_init,
"Supported page size register = 0x%x", page_size);
-   for (i = 0; i < 16; i++) {
-   if ((0x1 & page_size) != 0)
-   break;
-   page_size = page_size >> 1;
-   }
+   i = ffs(page_size);
if (i < 16)
xhci_dbg_trace(xhci, trace_xhci_dbg_init,
"Supported page size of %iK", (1 << (i+12)) / 1024);


Hi

using ffs() is a welcome change, but it will give different a result than the 
loop.

*old loop
valid page_size value if i < 16
*ffs()
valid page_size value if i >= 1 and i < 17


off-by-one, just use i = ffs() - 1. Or use __ffs().



and handle the page_size == 0 case.

-Mathias  

Re: [PATCH] xhci: Use ffs() to find page size in xhci_mem_init()

[Felipe Balbi]

Hi,

Mathias Nyman  writes:
> On 07.02.2019 02:03, Andrey Smirnov wrote:
>> Get page size order using ffs() instead of open coding it with a loop.
>> 
>> Signed-off-by: Andrey Smirnov 
>> Cc: Mathias Nyman 
>> Cc: Greg Kroah-Hartman 
>> Cc: linux-...@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>> ---
>>   drivers/usb/host/xhci-mem.c | 6 +-
>>   1 file changed, 1 insertion(+), 5 deletions(-)
>> 
>> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
>> index 36a3eb8849f1..44b43c3d819f 100644
>> --- a/drivers/usb/host/xhci-mem.c
>> +++ b/drivers/usb/host/xhci-mem.c
>> @@ -2362,11 +2362,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
>>  page_size = readl(>op_regs->page_size);
>>  xhci_dbg_trace(xhci, trace_xhci_dbg_init,
>>  "Supported page size register = 0x%x", page_size);
>> -for (i = 0; i < 16; i++) {
>> -if ((0x1 & page_size) != 0)
>> -break;
>> -page_size = page_size >> 1;
>> -}
>> +i = ffs(page_size);
>>  if (i < 16)
>>  xhci_dbg_trace(xhci, trace_xhci_dbg_init,
>>  "Supported page size of %iK", (1 << (i+12)) / 1024);
>
> Hi
>
> using ffs() is a welcome change, but it will give different a result than the 
> loop.
>
> *old loop
>valid page_size value if i < 16
> *ffs()
>valid page_size value if i >= 1 and i < 17

off-by-one, just use i = ffs() - 1. Or use __ffs().

-- 
balbi


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Description: PGP signature

Re: [PATCH] xhci: Use ffs() to find page size in xhci_mem_init()

[Mathias Nyman]

On 07.02.2019 02:03, Andrey Smirnov wrote:

Get page size order using ffs() instead of open coding it with a loop.

Signed-off-by: Andrey Smirnov 
Cc: Mathias Nyman 
Cc: Greg Kroah-Hartman 
Cc: linux-...@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
  drivers/usb/host/xhci-mem.c | 6 +-
  1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 36a3eb8849f1..44b43c3d819f 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -2362,11 +2362,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
page_size = readl(>op_regs->page_size);
xhci_dbg_trace(xhci, trace_xhci_dbg_init,
"Supported page size register = 0x%x", page_size);
-   for (i = 0; i < 16; i++) {
-   if ((0x1 & page_size) != 0)
-   break;
-   page_size = page_size >> 1;
-   }
+   i = ffs(page_size);
if (i < 16)
xhci_dbg_trace(xhci, trace_xhci_dbg_init,
"Supported page size of %iK", (1 << (i+12)) / 1024);


Hi

using ffs() is a welcome change, but it will give different a result than the 
loop.

*old loop
  valid page_size value if i < 16
*ffs()
  valid page_size value if i >= 1 and i < 17
 
-Mathias


 

[PATCH] xhci: Use ffs() to find page size in xhci_mem_init()

[Andrey Smirnov]

Get page size order using ffs() instead of open coding it with a loop.

Signed-off-by: Andrey Smirnov 
Cc: Mathias Nyman 
Cc: Greg Kroah-Hartman 
Cc: linux-...@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/usb/host/xhci-mem.c | 6 +-
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 36a3eb8849f1..44b43c3d819f 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -2362,11 +2362,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
page_size = readl(>op_regs->page_size);
xhci_dbg_trace(xhci, trace_xhci_dbg_init,
"Supported page size register = 0x%x", page_size);
-   for (i = 0; i < 16; i++) {
-   if ((0x1 & page_size) != 0)
-   break;
-   page_size = page_size >> 1;
-   }
+   i = ffs(page_size);
if (i < 16)
xhci_dbg_trace(xhci, trace_xhci_dbg_init,
"Supported page size of %iK", (1 << (i+12)) / 1024);
-- 
2.20.1