From mboxrd@z Thu Jan 1 00:00:00 1970 From: marek.vasut@gmail.com (Marek Vasut) Date: Thu, 7 Mar 2019 12:14:06 +0100 Subject: [PATCH 1/2] [RFC] ata: ahci: Respect bus DMA constraints In-Reply-To: <79e44e90-b16a-5315-e02f-101a2ebbb6a0@arm.com> References: <20190307000440.8708-1-marek.vasut@gmail.com> <7c051bbd-7835-9cab-30b2-0acde1364781@arm.com> <356f3ee8-407f-f865-e5cc-333695d4f857@gmail.com> <79e44e90-b16a-5315-e02f-101a2ebbb6a0@arm.com> Message-ID: On 3/7/19 10:48 AM, Robin Murphy wrote: > On 2019-03-07 9:37 am, Marek Vasut wrote: >> On 3/7/19 10:32 AM, Robin Murphy wrote: >>> On 2019-03-07 12:04 am, marek.vasut@gmail.com wrote: >>>> From: Marek Vasut >>>> >>>> Since commit 6c2fb2ea7636 ("of/device: Set bus DMA mask as >>>> appropriate"), >>>> the upstream bus can constraint device DMA range. Respect that >>>> constraint >>>> and do not change the device DMA masks if they were already set. >>>> >>>> This is applicable e.g. on systems where the PCIe controller cannot >>>> expose >>>> the full address space range. Such a system may have a 64bit CPU with >>>> DRAM >>>> mapped both below and above the 32bit address space, yet the PCIe >>>> devices >>>> can not perform DMA directly to/from the DRAM range above the 32bit >>>> limit. >>>> Hence, for such setup to work, all the buffers must exist below the >>>> 32bit >>>> limit. >>>> >>>> Signed-off-by: Marek Vasut >>>> Cc: Christoph Hellwig >>>> Cc: Geert Uytterhoeven >>>> Cc: Jens Axboe >>>> Cc: Jens Axboe >>>> Cc: Keith Busch >>>> Cc: Robin Murphy >>>> Cc: Sagi Grimberg >>>> Cc: Wolfram Sang >>>> Cc: linux-renesas-soc at vger.kernel.org >>>> To: linux-ide at vger.kernel.org >>>> To: linux-nvme at lists.infradead.org >>>> --- >>>> ?? drivers/ata/ahci.c | 7 +++++++ >>>> ?? 1 file changed, 7 insertions(+) >>>> >>>> diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c >>>> index 021ce46e2e57..2acce056dd8c 100644 >>>> --- a/drivers/ata/ahci.c >>>> +++ b/drivers/ata/ahci.c >>>> @@ -926,6 +926,13 @@ static int ahci_configure_dma_masks(struct >>>> pci_dev *pdev, int using_dac) >>>> ?????? if (pdev->dma_mask && pdev->dma_mask < DMA_BIT_MASK(32)) >>>> ?????????? return 0; >>>> ?? +??? /* >>>> +???? * The upstream device could have applied DMA constraints already, >>>> +???? * respect those and do not change the DMA masks. >>>> +???? */ >>>> +??? if (pdev->dev.dma_mask && pdev->dev.coherent_dma_mask) >>>> +??????? return 0; >>> >>> At least for DT platforms, the device masks are always going to be set >>> to some initial value, which will most commonly just be the 32-bit >>> default - that should not prevent the driver from setting wider masks if >>> that's what the device really supports (in fact there are some patches >>> queued in which we're now starting to formalise that properly). >>> >>> Are you seeing a problem with a DMA API backend failing to respect >>> bus_dma_mask? >> >> Yes, the DMA mask gets overridden here to 64bit one, which on the R-Car >> Gen3 with PCI with 32bit addressing limitation makes the AHCI driver >> fail (and NVMe driver, and xHCI PCI etc). All those PCI devices fail the >> same way because they override the DMA mask. > > Right, but whoever *interprets* the device masks after the driver has > overridden them should be taking the (smaller) bus mask into account as > well, so the question is where is *that* not being done correctly? Do you have a hint where I should look for that ? -- Best regards, Marek Vasut