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Date:   Wed, 14 Dec 2022 23:13:41 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc:     Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
        Vinod Koul <vkoul@kernel.org>, Rob Herring <robh@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Cai Huoqing <cai.huoqing@linux.dev>,
        Robin Murphy <robin.murphy@arm.com>,
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        Lorenzo Pieralisi <lpieralisi@kernel.org>,
        Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>,
        Serge Semin <fancer.lancer@gmail.com>,
        Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@baikalelectronics.ru>,
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        linux-pci@vger.kernel.org, dmaengine@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 23/25] PCI: dwc: Restore DMA-mask after MSI-data
 allocation
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References: <20221214235305.31744-1-Sergey.Semin@baikalelectronics.ru>
 <20221214235305.31744-24-Sergey.Semin@baikalelectronics.ru>
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On Thu, Dec 15, 2022 at 02:53:03AM +0300, Serge Semin wrote:
> DW PCIe Root Ports and End-points can be equipped with the DW eDMA engine.
> In that case it is critical to have the platform device pre-initialized
> with a valid DMA-mask so the drivers using the eDMA-engine would be able
> to allocate the DMA-able buffers. The MSI-capable data requires to be
> allocated from the lowest 4GB region. Since that procedure implies the
> DMA-mask change we need to restore the mask set by the low-level drivers
> after the MSI-data allocation is done.

You can't change the DMA mask when there are existing allocations.