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SubjectRe: [PATCH 1/2] coresight: tmc-etr: Correct memory sync ranges in SG mode
On Mon, Jul 12, 2021 at 11:25:54AM +0100, Suzuki Kuruppassery Poulose wrote:
> Hi Leo,
>
> On 10/07/2021 08:02, Leo Yan wrote:
> > Current code syncs the buffer range is [offset, offset+len), it doesn't
> > consider the case when the trace data is wrapped around, in this case
> > 'offset+len' is bigger than 'etr_buf->size'. Thus it syncs buffer out
> > of the memory buffer, and it also misses to sync buffer from the start
> > of the memory.
> >
>
> I doubt this claim is valid. We do the sync properly, taking the page
> corresponding to the "offset" wrapping it around in "page" index.
>
> Here is the code :
>
>
>
> void tmc_sg_table_sync_data_range(struct tmc_sg_table *table,
> u64 offset, u64 size)
> {
> int i, index, start;
> int npages = DIV_ROUND_UP(size, PAGE_SIZE);
> struct device *real_dev = table->dev->parent;
> struct tmc_pages *data = &table->data_pages;
>
> start = offset >> PAGE_SHIFT;
> for (i = start; i < (start + npages); i++) {
> index = i % data->nr_pages;
> dma_sync_single_for_cpu(real_dev, data->daddrs[index],
> PAGE_SIZE, DMA_FROM_DEVICE);
> }
> }
>
>
> See that the npages accounts for the "size" requested and we wrap the
> "index" by the total number of pages in the buffer and pick the right
> page.
>
> So, I think this fix is not needed.

Ouch, you are right :) Let's drop these two patches.

Thanks,
Leo

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