linux-kernel - Re: [PATCH 4/5] [SCSI] Do not use platform

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Date:	Fri, 01 Aug 2014 18:25:24 +0100
From:	Pawel Moll <pawel.moll@....com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Olof Johansson <olof@...om.net>,
	Stephen Warren <swarren@...dotorg.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"paul@...an.com" <paul@...an.com>, Arnd Bergmann <arnd@...db.de>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	"arm@...nel.org" <arm@...nel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH 4/5] [SCSI] Do not use platform_bus as a parent

On Sun, 2014-07-27 at 16:07 +0100, Greg Kroah-Hartman wrote:
> Ah, ok, it's a scsi core thing, not a driver core thing, that's less
> confusing now.  For a "fallback" of a platform device, if you switch the
> lines around you should be fine, something like this patch perhaps:
> 
> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> index 3cbb57a8b846..d8d3b294f5bc 100644
> --- a/drivers/scsi/hosts.c
> +++ b/drivers/scsi/hosts.c
> @@ -218,16 +218,16 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
>  		goto fail;
>  
>  	if (!shost->shost_gendev.parent)
> -		shost->shost_gendev.parent = dev ? dev : &platform_bus;
> -	if (!dma_dev)
> -		dma_dev = shost->shost_gendev.parent;
> -
> -	shost->dma_dev = dma_dev;
> +		shost->shost_gendev.parent = dev;
>  
>  	error = device_add(&shost->shost_gendev);
>  	if (error)
>  		goto out;
>  
> +	if (!dma_dev)
> +		dma_dev = shost->shost_gendev.parent;
> +	shost->dma_dev = dma_dev;
> +
>  	pm_runtime_set_active(&shost->shost_gendev);
>  	pm_runtime_enable(&shost->shost_gendev);
>  	device_enable_async_suspend(&shost->shost_gendev);

But this will still make shost->dma_dev == NULL in the cases James
quoted:

On Fri, 2014-07-25 at 15:46 +0100, James Bottomley wrote:
> Yes, for DMA purposes, the parent cannot now be NULL; we'll get a panic
> in the DMA transfers if it is.  A lot of the legacy ISA device on x86
> and I thought some ARM SOC devices don't pass in the parent device, so
> we hang them off a known parent.
> 
> You can grep for it; these are the devices that will begin to panic if
> you apply this patch:
> 
> arch/ia64/hp/sim/simscsi.c:     error = scsi_add_host(host, NULL);
> drivers/scsi/a2091.c:   error = scsi_add_host(instance, NULL);
> drivers/scsi/a3000.c:   error = scsi_add_host(instance, NULL);
> drivers/scsi/aha152x.c: if( scsi_add_host(shpnt, NULL) ) {
> drivers/scsi/gdth.c:    error = scsi_add_host(shp, NULL);
> drivers/scsi/gdth.c:    error = scsi_add_host(shp, NULL);
> drivers/scsi/gvp11.c:   error = scsi_add_host(instance, NULL);
> drivers/scsi/imm.c:     err = scsi_add_host(host, NULL);
> drivers/scsi/pcmcia/fdomain_stub.c:    if (scsi_add_host(host, NULL))
> drivers/scsi/pcmcia/nsp_cs.c:   ret = scsi_add_host (host, NULL);
> drivers/scsi/pcmcia/qlogic_stub.c:      if (scsi_add_host(shost, NULL))
> drivers/scsi/pcmcia/sym53c500_cs.c:     if (scsi_add_host(host, NULL))
> drivers/scsi/ppa.c:     err = scsi_add_host(host, NULL);
> drivers/scsi/qlogicfas.c:       if (scsi_add_host(hreg, NULL))
> drivers/scsi/scsi_module.c:             error = scsi_add_host(shost, NULL);
> drivers/scsi/sgiwd93.c: err = scsi_add_host(host, NULL);

Maybe the DMA API should be coping with NULL device? It seems to handle
it in a half of the methods and fails in the other half...

Pawel

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