Re: [PATCH] drm/ast: Fixed system hanged if disable P2A

[Benjamin Herrenschmidt <benh@au1.ibm.com>]

On Thu, 2017-02-16 at 06:34 +0000, YC Chen wrote:
> Hi Ben,
> This solution had been proved on x86 platform but I'm not sure if it
> works or not on POWER system .

It will only work on x86 platforms that haven't configured their
PCI Express in "hardened" mode where PCIe errors cause machine checks
or worse.

That said there isn't much I can do about it for now. So for POWER
platforms (and other platforms using device-tree), I have a patch
that will get the data from there.

>  If we added a definition in SOC scratch register to info drm driver
> the P2A is disabled by BMC fw, then drm driver will no need to check
> it by reading 0xf00x. Is it acceptable?

It would be better yes. Please send me a patch as I've reworked yours
already (see what i'll post tomorrow). Additionally, for future
silicon, please make all those info necessary to detect the VRAM
and the PLL available via the VGA registers so the backdoor isn't
needed.

For a full POST we can still require it of course but for the normal
case we should be able to get all the info needed via the normal VGA
register space.

> Here are the flow:
> If disable P2A in SOC scratch then ast->DisableP2A = true;
> Else if the value of 0xf00x is not 0xFFFF_FFFF then ast->DisableP2A =
> false;

Cheers,
Ben.

> Regards,
> 
> Y.C. Chen
> 
> -----Original Message-----
> From: Benjamin Herrenschmidt [mailto:benh@au1.ibm.com] 
> Sent: Thursday, February 16, 2017 11:58 AM
> To: YC Chen <yc_chen@aspeedtech.com>; dri-devel@lists.freedesktop.org
> Cc: airlied@redhat.com; eich@suse.com; Russell Currey <ruscur@au1.ibm
> .com>
> Subject: Re: [PATCH] drm/ast: Fixed system hanged if disable P2A
> 
> On Thu, 2017-01-26 at 09:45 +0800, Y.C. Chen wrote:
> > From: "Y.C. Chen" <yc_chen@aspeedtech.com>
> > 
> > The original ast driver will access some BMC configuration through
> > P2A 
> > bridge that can be disabled since AST2300 and after.
> > It will cause system hanged if P2A bridge is disabled.
> > Here is the update to fix it.
> 
> Will this work for us on POWER ? The problem we observed is that if
> P2A is disabled, the read from f00x seems to not respond, ie, we get
> a PCIe target abort on the MMIO, not 0xffff_ffff. That trips our HW
> error detection mechanism "EEH" which will take out the entire
> device.
> 
> Russell (CC) proposed a patch a while ago that seems to have gone
> nowhere that allows the driver to retrieve all the information it
> needs from the device-tree on platforms that support it.
> 
> That allows us to grab the necessary info from firmware before the
> bridge is closed (or via some specific BMC interface we have if we
> close the bridge) and pass it to Linux.
> 
> Any reason that patch hasn't been merged ? Dave ?
> 
> Cheers,
> Ben.
> 
> 
> > Signed-off-by: Y.C. Chen <yc_chen@aspeedtech.com>
> > ---
> >  drivers/gpu/drm/ast/ast_drv.h  |   1 +
> >  drivers/gpu/drm/ast/ast_main.c | 156 ++++++++++++++++++++++-------
> > --
> > ----------
> >  drivers/gpu/drm/ast/ast_post.c |  18 +++--
> >  3 files changed, 96 insertions(+), 79 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/ast/ast_drv.h 
> > b/drivers/gpu/drm/ast/ast_drv.h index 908011d..7abda94 100644
> > --- a/drivers/gpu/drm/ast/ast_drv.h
> > +++ b/drivers/gpu/drm/ast/ast_drv.h
> > @@ -113,6 +113,7 @@ struct ast_private {
> >  	struct ttm_bo_kmap_obj cache_kmap;
> >  	int next_cursor;
> >  	bool support_wide_screen;
> > +	bool DisableP2A;
> >  
> >  	enum ast_tx_chip tx_chip_type;
> >  	u8 dp501_maxclk;
> > diff --git a/drivers/gpu/drm/ast/ast_main.c 
> > b/drivers/gpu/drm/ast/ast_main.c index f75c642..c374685 100644
> > --- a/drivers/gpu/drm/ast/ast_main.c
> > +++ b/drivers/gpu/drm/ast/ast_main.c
> > @@ -124,6 +124,11 @@ static int ast_detect_chip(struct drm_device 
> > *dev, bool *need_post)
> >  	} else
> >  		*need_post = false;
> >  
> > +	/* Check P2A Access */
> > +	ast->DisableP2A = true;
> > +	data = ast_read32(ast, 0xf004);
> > +	if (data != 0xFFFFFFFF) ast->DisableP2A = false;
> > +
> >  	/* Check if we support wide screen */
> >  	switch (ast->chip) {
> >  	case AST1180:
> > @@ -140,15 +145,17 @@ static int ast_detect_chip(struct drm_device 
> > *dev, bool *need_post)
> >  			ast->support_wide_screen = true;
> >  		else {
> >  			ast->support_wide_screen = false;
> > -			/* Read SCU7c (silicon revision register)
> > */
> > -			ast_write32(ast, 0xf004, 0x1e6e0000);
> > -			ast_write32(ast, 0xf000, 0x1);
> > -			data = ast_read32(ast, 0x1207c);
> > -			data &= 0x300;
> > -			if (ast->chip == AST2300 && data == 0x0)
> > /*
> > ast1300 */
> > -				ast->support_wide_screen = true;
> > -			if (ast->chip == AST2400 && data == 0x100)
> > /* ast1400 */
> > -				ast->support_wide_screen = true;
> > +			if (ast->DisableP2A == false) {
> > +				/* Read SCU7c (silicon revision
> > register) */
> > +				ast_write32(ast, 0xf004,
> > 0x1e6e0000);
> > +				ast_write32(ast, 0xf000, 0x1);
> > +				data = ast_read32(ast, 0x1207c);
> > +				data &= 0x300;
> > +				if (ast->chip == AST2300 && data
> > ==
> > 0x0) /* ast1300 */
> > +					ast->support_wide_screen =
> > true;
> > +				if (ast->chip == AST2400 && data
> > ==
> > 0x100) /* ast1400 */
> > +					ast->support_wide_screen =
> > true;
> > +			}
> >  		}
> >  		break;
> >  	}
> > @@ -216,80 +223,81 @@ static int ast_get_dram_info(struct
> > drm_device
> > *dev)
> >  	uint32_t data, data2;
> >  	uint32_t denum, num, div, ref_pll;
> >  
> > -	ast_write32(ast, 0xf004, 0x1e6e0000);
> > -	ast_write32(ast, 0xf000, 0x1);
> > -
> > -
> > -	ast_write32(ast, 0x10000, 0xfc600309);
> > -
> > -	do {
> > -		if (pci_channel_offline(dev->pdev))
> > -			return -EIO;
> > -	} while (ast_read32(ast, 0x10000) != 0x01);
> > -	data = ast_read32(ast, 0x10004);
> > -
> > -	if (data & 0x40)
> > +	if (ast->DisableP2A)
> > +	{
> >  		ast->dram_bus_width = 16;
> > +		ast->dram_type = AST_DRAM_1Gx16;
> > +		ast->mclk = 396;
> > +	}
> >  	else
> > -		ast->dram_bus_width = 32;
> > +	{
> > +		ast_write32(ast, 0xf004, 0x1e6e0000);
> > +		ast_write32(ast, 0xf000, 0x1);
> > +		data = ast_read32(ast, 0x10004);
> > +
> > +		if (data & 0x40)
> > +			ast->dram_bus_width = 16;
> > +		else
> > +			ast->dram_bus_width = 32;
> > +
> > +		if (ast->chip == AST2300 || ast->chip == AST2400)
> > {
> > +			switch (data & 0x03) {
> > +			case 0:
> > +				ast->dram_type = AST_DRAM_512Mx16;
> > +				break;
> > +			default:
> > +			case 1:
> > +				ast->dram_type = AST_DRAM_1Gx16;
> > +				break;
> > +			case 2:
> > +				ast->dram_type = AST_DRAM_2Gx16;
> > +				break;
> > +			case 3:
> > +				ast->dram_type = AST_DRAM_4Gx16;
> > +				break;
> > +			}
> > +		} else {
> > +			switch (data & 0x0c) {
> > +			case 0:
> > +			case 4:
> > +				ast->dram_type = AST_DRAM_512Mx16;
> > +				break;
> > +			case 8:
> > +				if (data & 0x40)
> > +					ast->dram_type =
> > AST_DRAM_1Gx16;
> > +				else
> > +					ast->dram_type =
> > AST_DRAM_512Mx32;
> > +				break;
> > +			case 0xc:
> > +				ast->dram_type = AST_DRAM_1Gx32;
> > +				break;
> > +			}
> > +		}
> >  
> > -	if (ast->chip == AST2300 || ast->chip == AST2400) {
> > -		switch (data & 0x03) {
> > -		case 0:
> > -			ast->dram_type = AST_DRAM_512Mx16;
> > -			break;
> > -		default:
> > -		case 1:
> > -			ast->dram_type = AST_DRAM_1Gx16;
> > -			break;
> > -		case 2:
> > -			ast->dram_type = AST_DRAM_2Gx16;
> > -			break;
> > +		data = ast_read32(ast, 0x10120);
> > +		data2 = ast_read32(ast, 0x10170);
> > +		if (data2 & 0x2000)
> > +			ref_pll = 14318;
> > +		else
> > +			ref_pll = 12000;
> > +
> > +		denum = data & 0x1f;
> > +		num = (data & 0x3fe0) >> 5;
> > +		data = (data & 0xc000) >> 14;
> > +		switch (data) {
> >  		case 3:
> > -			ast->dram_type = AST_DRAM_4Gx16;
> > -			break;
> > -		}
> > -	} else {
> > -		switch (data & 0x0c) {
> > -		case 0:
> > -		case 4:
> > -			ast->dram_type = AST_DRAM_512Mx16;
> > +			div = 0x4;
> >  			break;
> > -		case 8:
> > -			if (data & 0x40)
> > -				ast->dram_type = AST_DRAM_1Gx16;
> > -			else
> > -				ast->dram_type = AST_DRAM_512Mx32;
> > +		case 2:
> > +		case 1:
> > +			div = 0x2;
> >  			break;
> > -		case 0xc:
> > -			ast->dram_type = AST_DRAM_1Gx32;
> > +		default:
> > +			div = 0x1;
> >  			break;
> >  		}
> > +		ast->mclk = ref_pll * (num + 2) / (denum + 2) *
> > (div
> > * 1000);
> >  	}
> > -
> > -	data = ast_read32(ast, 0x10120);
> > -	data2 = ast_read32(ast, 0x10170);
> > -	if (data2 & 0x2000)
> > -		ref_pll = 14318;
> > -	else
> > -		ref_pll = 12000;
> > -
> > -	denum = data & 0x1f;
> > -	num = (data & 0x3fe0) >> 5;
> > -	data = (data & 0xc000) >> 14;
> > -	switch (data) {
> > -	case 3:
> > -		div = 0x4;
> > -		break;
> > -	case 2:
> > -	case 1:
> > -		div = 0x2;
> > -		break;
> > -	default:
> > -		div = 0x1;
> > -		break;
> > -	}
> > -	ast->mclk = ref_pll * (num + 2) / (denum + 2) * (div *
> > 1000);
> >  	return 0;
> >  }
> >  
> > diff --git a/drivers/gpu/drm/ast/ast_post.c 
> > b/drivers/gpu/drm/ast/ast_post.c index 810c51d..5331ee1 100644
> > --- a/drivers/gpu/drm/ast/ast_post.c
> > +++ b/drivers/gpu/drm/ast/ast_post.c
> > @@ -379,12 +379,20 @@ void ast_post_gpu(struct drm_device *dev)
> >  	ast_open_key(ast);
> >  	ast_set_def_ext_reg(dev);
> >  
> > -	if (ast->chip == AST2300 || ast->chip == AST2400)
> > -		ast_init_dram_2300(dev);
> > -	else
> > -		ast_init_dram_reg(dev);
> > +	if (ast->DisableP2A == false)
> > +	{
> > +		if (ast->chip == AST2300 || ast->chip == AST2400)
> > +			ast_init_dram_2300(dev);
> > +		else
> > +			ast_init_dram_reg(dev);
> >  
> > -	ast_init_3rdtx(dev);
> > +		ast_init_3rdtx(dev);
> > +	}
> > +	else
> > +	{
> > +		if (ast->tx_chip_type != AST_TX_NONE)
> > +			ast_set_index_reg_mask(ast,
> > AST_IO_CRTC_PORT, 0xa3, 0xcf, 0x80);	/* Enable DVO */
> > +	}
> >  }
> >  
> >  /* AST 2300 DRAM settings */
> 
> 

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