> Am 11.04.2018 um 11:12 schrieb Ladislav Michl <la...@linux-mips.org>:
>
> On Wed, Apr 11, 2018 at 10:52:01AM +0200, Boris Brezillon wrote:
>> On Wed, 11 Apr 2018 10:27:46 +0200
>> Ladislav Michl <la...@linux-mips.org> wrote:
>>
>>> On Wed, Apr 11, 2018 at 10:08:06AM +0200, Boris Brezillon wrote:
>>>> On Wed, 11 Apr 2018 09:36:56 +0200
>>>> Ladislav Michl <la...@linux-mips.org> wrote:
>>>>
>>>>> Hi Boris,
>>>>>
>>>>> On Wed, Apr 11, 2018 at 09:15:28AM +0200, Boris Brezillon wrote:
>>> [...]
>>>>>> Not sure this approach is safe on all archs: if the cache is VIVT or
>>>>>> VIPT, you may have several entries pointing to the same phys page, and
>>>>>> then, when dma_map_page() does its cache maintenance operations, it's
>>>>>> only taking one of these entries into account.
>>>>>
>>>>> Hmm, I used the same approach Samsung OneNAND driver does since commit
>>>>> dcf08227e964a53a2cb39130b74842c7dcb6adde.
>>>>> Both TI OMAP3630 and Samsung S5PC110 are using Cortex-A8 which
>>>>> is VIPT. In that case samsung's driver code has the same problem.
>>>>>
>>>>>> In other parts of the MTD subsystem, we tend to not do DMA on buffers
>>>>>> that have been vmalloc-ed.
>>>>>>
>>>>>> You can do something like
>>>>>>
>>>>>> if (virt_addr_valid(buf))
>>>>>> /* Use DMA */
>>>>>> else
>>>>>> /*
>>>>>> * Do not use DMA, or use a bounce buffer
>>>>>> * allocated with kmalloc
>>>>>> */
>>>>>
>>>>> Okay, I'll use this approach then, but first I'd like to be sure above is
>>>>> correct. Anyone?
>>>>
>>>> See this discussion [1]. The problem came up a few times already, so
>>>> might find other threads describing why it's not safe.
>>>>
>>>> [1]https://lists.linuxfoundation.org/pipermail/iommu/2016-March/016240.html
>>>>
>>>
>>> Question was more likely whenever there might exist more that one mapping
>>> of the same page.
>>
>> I'm clearly not an expert, so I might be wrong, but I think a physical
>> page can be both in the identity mapping and mapped in the vmalloc
>> space. Now, is there a real risk that both ends are accessed in
>> parallel thus making different cache entries pointing to the same phys
>> page dirty, I'm not sure. Or maybe there are other corner case, but
>> you'll have to ask Russell (or any other ARM expert) to get a clearer
>> answer.
>
> Thank you anyway. As DMA was disabled completely for all DT enabled boards
> until 4.16 let's play safe and disable it for HIGHMEM case as you suggested.
> Later, we might eventually use the same {read,write}_bufferram for both
> OMAP and S5PC110.
>
>>> But okay, I'll disable DMA for highmem. Patch will follow.
>>>
>>> ladis
>
> Andreas, Nikolaus, could you please test patch bellow? It is against
> linux.git and should apply also against 4.16 once you modify path.
Works with v4.16!
I have done "tar cf /dev/null /mnt/nand" and have only
got some fixable bit flips. Writing a test file to OneNAND
also worked and doing a sync did move the weak block to a new PEB.
So I think read & write works again.
>
> Thank you,
> ladis
BR and thanks,
Nikolaus
>
> --- >8 ---
>
> From: Ladislav Michl <la...@linux-mips.org>
> Subject: [PATCH] mtd: onenand: omap2: Disable DMA for HIGHMEM buffers
>
> dma_map_single doesn't get the proper DMA address for vmalloced area,
> so disable DMA in this case.
>
> Signed-off-by: Ladislav Michl <la...@linux-mips.org>
> Reported-by: "H. Nikolaus Schaller" <h...@goldelico.com>
> ---
> drivers/mtd/nand/onenand/omap2.c | 105 +++++++++++--------------------
> 1 file changed, 38 insertions(+), 67 deletions(-)
>
> diff --git a/drivers/mtd/nand/onenand/omap2.c
> b/drivers/mtd/nand/onenand/omap2.c
> index 9c159f0dd9a6..321137158ff3 100644
> --- a/drivers/mtd/nand/onenand/omap2.c
> +++ b/drivers/mtd/nand/onenand/omap2.c
> @@ -375,56 +375,42 @@ static int omap2_onenand_read_bufferram(struct mtd_info
> *mtd, int area,
> {
> struct omap2_onenand *c = container_of(mtd, struct omap2_onenand, mtd);
> struct onenand_chip *this = mtd->priv;
> - dma_addr_t dma_src, dma_dst;
> - int bram_offset;
> + struct device *dev = &c->pdev->dev;
> void *buf = (void *)buffer;
> + dma_addr_t dma_src, dma_dst;
> + int bram_offset, err;
> size_t xtra;
> - int ret;
>
> bram_offset = omap2_onenand_bufferram_offset(mtd, area) + area + offset;
> - if (bram_offset & 3 || (size_t)buf & 3 || count < 384)
> - goto out_copy;
> -
> - /* panic_write() may be in an interrupt context */
> - if (in_interrupt() || oops_in_progress)
> + /*
> + * If the buffer address is not DMA-able, len is not long enough to make
> + * DMA transfers profitable or panic_write() may be in an interrupt
> + * context fallback to PIO mode.
> + */
> + if (!virt_addr_valid(buf) || bram_offset & 3 || (size_t)buf & 3 ||
> + count < 384 || in_interrupt() || oops_in_progress )
> goto out_copy;
>
> - if (buf >= high_memory) {
> - struct page *p1;
> -
> - if (((size_t)buf & PAGE_MASK) !=
> - ((size_t)(buf + count - 1) & PAGE_MASK))
> - goto out_copy;
> - p1 = vmalloc_to_page(buf);
> - if (!p1)
> - goto out_copy;
> - buf = page_address(p1) + ((size_t)buf & ~PAGE_MASK);
> - }
> -
> xtra = count & 3;
> if (xtra) {
> count -= xtra;
> memcpy(buf + count, this->base + bram_offset + count, xtra);
> }
>
> + dma_dst = dma_map_single(dev, buf, count, DMA_FROM_DEVICE);
> dma_src = c->phys_base + bram_offset;
> - dma_dst = dma_map_single(&c->pdev->dev, buf, count, DMA_FROM_DEVICE);
> - if (dma_mapping_error(&c->pdev->dev, dma_dst)) {
> - dev_err(&c->pdev->dev,
> - "Couldn't DMA map a %d byte buffer\n",
> - count);
> - goto out_copy;
> - }
>
> - ret = omap2_onenand_dma_transfer(c, dma_src, dma_dst, count);
> - dma_unmap_single(&c->pdev->dev, dma_dst, count, DMA_FROM_DEVICE);
> -
> - if (ret) {
> - dev_err(&c->pdev->dev, "timeout waiting for DMA\n");
> + if (dma_mapping_error(dev, dma_dst)) {
> + dev_err(dev, "Couldn't DMA map a %d byte buffer\n", count);
> goto out_copy;
> }
>
> - return 0;
> + err = omap2_onenand_dma_transfer(c, dma_src, dma_dst, count);
> + dma_unmap_single(dev, dma_dst, count, DMA_FROM_DEVICE);
> + if (!err)
> + return 0;
> +
> + dev_err(dev, "timeout waiting for DMA\n");
>
> out_copy:
> memcpy(buf, this->base + bram_offset, count);
> @@ -437,49 +423,34 @@ static int omap2_onenand_write_bufferram(struct
> mtd_info *mtd, int area,
> {
> struct omap2_onenand *c = container_of(mtd, struct omap2_onenand, mtd);
> struct onenand_chip *this = mtd->priv;
> - dma_addr_t dma_src, dma_dst;
> - int bram_offset;
> + struct device *dev = &c->pdev->dev;
> void *buf = (void *)buffer;
> - int ret;
> + dma_addr_t dma_src, dma_dst;
> + int bram_offset, err;
>
> bram_offset = omap2_onenand_bufferram_offset(mtd, area) + area + offset;
> - if (bram_offset & 3 || (size_t)buf & 3 || count < 384)
> - goto out_copy;
> -
> - /* panic_write() may be in an interrupt context */
> - if (in_interrupt() || oops_in_progress)
> + /*
> + * If the buffer address is not DMA-able, len is not long enough to make
> + * DMA transfers profitable or panic_write() may be in an interrupt
> + * context fallback to PIO mode.
> + */
> + if (!virt_addr_valid(buf) || bram_offset & 3 || (size_t)buf & 3 ||
> + count < 384 || in_interrupt() || oops_in_progress )
> goto out_copy;
>
> - if (buf >= high_memory) {
> - struct page *p1;
> -
> - if (((size_t)buf & PAGE_MASK) !=
> - ((size_t)(buf + count - 1) & PAGE_MASK))
> - goto out_copy;
> - p1 = vmalloc_to_page(buf);
> - if (!p1)
> - goto out_copy;
> - buf = page_address(p1) + ((size_t)buf & ~PAGE_MASK);
> - }
> -
> - dma_src = dma_map_single(&c->pdev->dev, buf, count, DMA_TO_DEVICE);
> + dma_src = dma_map_single(dev, buf, count, DMA_TO_DEVICE);
> dma_dst = c->phys_base + bram_offset;
> - if (dma_mapping_error(&c->pdev->dev, dma_src)) {
> - dev_err(&c->pdev->dev,
> - "Couldn't DMA map a %d byte buffer\n",
> - count);
> - return -1;
> - }
> -
> - ret = omap2_onenand_dma_transfer(c, dma_src, dma_dst, count);
> - dma_unmap_single(&c->pdev->dev, dma_src, count, DMA_TO_DEVICE);
> -
> - if (ret) {
> - dev_err(&c->pdev->dev, "timeout waiting for DMA\n");
> + if (dma_mapping_error(dev, dma_src)) {
> + dev_err(dev, "Couldn't DMA map a %d byte buffer\n", count);
> goto out_copy;
> }
>
> - return 0;
> + err = omap2_onenand_dma_transfer(c, dma_src, dma_dst, count);
> + dma_unmap_page(dev, dma_src, count, DMA_TO_DEVICE);
> + if (!err)
> + return 0;
> +
> + dev_err(dev, "timeout waiting for DMA\n");
>
> out_copy:
> memcpy(this->base + bram_offset, buf, count);
> --
> 2.17.0
>
