linux-kernel - RE: [PATCH] video: hyperv: hyperv_fb: Use physical memory for fb on HyperV Gen 1 VMs.

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Date:   Fri, 25 Oct 2019 08:09:34 +0000
From:   Wei Hu <weh@...rosoft.com>
To:     "hch@....de" <hch@....de>
CC:     "b.zolnierkie@...sung.com" <b.zolnierkie@...sung.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "mchehab+samsung@...nel.org" <mchehab+samsung@...nel.org>,
        "sam@...nborg.org" <sam@...nborg.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "alexandre.belloni@...tlin.com" <alexandre.belloni@...tlin.com>,
        "info@...ux.net" <info@...ux.net>, "arnd@...db.de" <arnd@...db.de>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Dexuan Cui <decui@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>
Subject: RE: [PATCH] video: hyperv: hyperv_fb: Use physical memory for fb on
 HyperV Gen 1 VMs.

Thanks for the review. Please see my response inline.

> > +	select DMA_CMA
> 
> Thіs needs to be
> 
> 	select DMA_CMA if HAVE_DMA_CONTIGUOUS
> 
> > +#include <linux/dma-contiguous.h>
> 
> > +	/* Allocate from CMA */
> > +	// request_pages = (request_size >> PAGE_SHIFT) + 1;
> > +	request_pages = (round_up(request_size, PAGE_SIZE) >> PAGE_SHIFT);
> > +	page = dma_alloc_from_contiguous(NULL, request_pages, 0, false);
> 
> dma_alloc_from_contiguous is an internal helper, you must use it
> through dma_alloc_coherent and pass a struct device to that function.
> 

Can I directly use cma_alloc() and cma_release() in this case? The contiguous
memory allocated is just for virtual framebuffer device, not for any DMA
operation. I think using dma_alloc_coherent() might be a bit of overkill.

> > +	if (!gen2vm) {
> > +		pdev = pci_get_device(PCI_VENDOR_ID_MICROSOFT,
> > +			PCI_DEVICE_ID_HYPERV_VIDEO, NULL);
> > +		if (!pdev) {
> > +			pr_err("Unable to find PCI Hyper-V video\n");
> > +			return -ENODEV;
> > +		}
> > +	}
> 
> Please actually implement a pci_driver instead of hacks like this.
> 

I don't quite follow this. What do you mean implementing a pci_driver
in this case?

> > +			par->need_docopy = false;
> > +			goto getmem1;
> > +		} else {
> 
> No need for an else after a goto.
Thanks. Will do.

Wei