On Fri, May 7, 2010 at 06:15, Oskar Schirmer wrote:
> On Thu, May 06, 2010 at 14:46:04 -0400, Mike Frysinger wrote:
>> On Thu, May 6, 2010 at 06:37, Oskar Schirmer wrote:
>> > struct ser_req {
>> > + u16 sample;
>> > + char __padalign[L1_CACHE_BYTES - sizeof(u16)];
>> > +
>> > u16 reset;
>> > u16 ref_on;
>> > u16 command;
>> > - u16 sample;
>> > struct spi_message msg;
>> > struct spi_transfer xfer[6];
>> > };
>>
>> are you sure this is necessary ? ser_req is only ever used with
>> spi_sync() and it's allocated/released on the fly, so how could
>> anything be reading that memory between the start of the transmission
>> and the return to adi7877 ?
>
> msg is handed over to spi_sync, it contains the addresses
> which will be used to programme the DMA: the spi master
> transfer function will read these fields to start DMA.
so the issue is coming from the SPI master drivers and not the AD7877 driver
>> > struct ad7877 {
>> > + u16 conversion_data[AD7877_NR_SENSE];
>> > + char __padalign[L1_CACHE_BYTES
>> > + - AD7877_NR_SENSE * sizeof(u16)];
>> > +
>> > struct input_dev *input;
>> > char phys[32];
>> >
>> > @@ -182,8 +188,6 @@ struct ad7877 {
>> > u8 averaging;
>> > u8 pen_down_acc_interval;
>> >
>> > - u16 conversion_data[AD7877_NR_SENSE];
>> > -
>> > struct spi_transfer xfer[AD7877_NR_SENSE + 2];
>> > struct spi_message msg;
>>
>> i can see the spi_message inside of this struct being a problem
>> because the spi transfer is doing asynchronously with spi_async().
>> however, i would add a comment right above these two fields with a
>> short explanation as to why they're at the start and why the pad
>> exists so someone down the line doesnt move it.
>
> The code says "pad to align according to L1 cache, and
> keep away other stuff by exactly the amount so it is
> off the line". I'ld guess a comment would repeat just
> this, so it is superfluous. But if opinions differ on
> this topic, we can have a comment added, sure.
not everyone knows to read every single piece of documentation that
may or may not be affected implicitly in the call stack. a simple
comment here is not superfluous.
since the other struct is also going to be changed, a comment should
be placed there as well.
-mike
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