[U-Boot] [PATCH v2 1/6] usb:gadget:ums: Replace malloc calls with memalign to fix cache buffer alignment

[Lukasz Majewski]

Hi Marek,

> On Thursday, February 06, 2014 at 07:33:07 AM, Lukasz Majewski wrote:
> > Hi Marek,
> > 
> > > On Wednesday, February 05, 2014 at 10:10:41 AM, Lukasz Majewski
> > > wrote:
> > > > Calls to malloc() have been replaced by memalign. It now
> > > > provides proper buffer alignment.
> > > > 
> > > > Signed-off-by: Lukasz Majewski <l.majewski at samsung.com>
> > > > Cc: Marek Vasut <marex at denx.de>
> > > > 
> > > > ---
> > > > Changes for v2:
> > > > - Remove Change-Id.
> > > > ---
> > > > 
> > > >  drivers/usb/gadget/f_mass_storage.c |    4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/usb/gadget/f_mass_storage.c
> > > > b/drivers/usb/gadget/f_mass_storage.c index b1fe8bd..f896169
> > > > 100644 --- a/drivers/usb/gadget/f_mass_storage.c
> > > > +++ b/drivers/usb/gadget/f_mass_storage.c
> > > > @@ -2515,7 +2515,7 @@ static struct fsg_common
> > > > 
> > > > *fsg_common_init(struct fsg_common *common, buffhds_first_it:
> > > >  		bh->inreq_busy = 0;
> > > >  		bh->outreq_busy = 0;
> > > > 
> > > > -		bh->buf = kmalloc(FSG_BUFLEN, GFP_KERNEL);
> > > > +		bh->buf = memalign(CONFIG_SYS_CACHELINE_SIZE,
> > > > FSG_BUFLEN); if (unlikely(!bh->buf)) {
> > > > 
> > > >  			rc = -ENOMEM;
> > > >  			goto error_release;
> > > > 
> > > > @@ -2622,7 +2622,7 @@ usb_copy_descriptors(struct
> > > > usb_descriptor_header **src) bytes += (*tmp)->bLength;
> > > > 
> > > >  	bytes += (n_desc + 1) * sizeof(*tmp);
> > > > 
> > > > -	mem = kmalloc(bytes, GFP_KERNEL);
> > > > +	mem = memalign(CONFIG_SYS_CACHELINE_SIZE, bytes);
> > > 
> > > I wonder, does this align the begining of the buffer as well or
> > > only the size? Can we rely on the fact the begining is also
> > > cacheline-aligned ?
> > 
> > In this case, the memalign assures, that beginning of the buffer is
> > aligned to a cache line.
> 
> How so ? :)

I'm just following what is written at ./include/malloc.h  :-)

memalign(size_t alignment, size_t n);
     Return a pointer to a newly allocated chunk of n bytes, aligned
     in accord with the alignment argument, which must be a power of
     two.

Usage of memalign seemed to fix the wrong cache alignment buffer
allocation issue in a code which I know.

> [...]
> 
> Best regards,
> Marek Vasut



-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group