linux-kernel - Re: [PATCH v7 23/25] PCI: dwc: Restore DMA-mask after MSI-data allocation

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Message-ID: <Y5rJJfZeVqliA5Rg@infradead.org>
Date:   Wed, 14 Dec 2022 23:13:41 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Vinod Koul <vkoul@...nel.org>, Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Cai Huoqing <cai.huoqing@...ux.dev>,
        Robin Murphy <robin.murphy@....com>,
        Jingoo Han <jingoohan1@...il.com>, Frank Li <Frank.Li@....com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        caihuoqing <caihuoqing@...du.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        linux-pci@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 23/25] PCI: dwc: Restore DMA-mask after MSI-data
 allocation

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.