Commit 486ff387 authored by Krzysztof Helt's avatar Krzysztof Helt Committed by Linus Torvalds
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cirrusfb: do not change MCLK for Alpine chips 



A memory clock value (MCLK) is changed to a minimum required by a current
mode bandwidth.  This usually lowers the MCLK to its minimum (50 MHz) thus
decreasing the card performance.  Just leave the MCLK value set by card
BIOS.

The CL-GD5446 Technical Reference Manual point 9.9.1.3 states that if a
pixclock value is close (~1%) to the MCLK or MCLK/2 this may result in a
jitter on the screen.  A countermeasure is to use the MCLK as pixclock
source instead of a VCLK.  The patch implements this as well.

Signed-off-by: default avatarKrzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3b921832

drivers/video/cirrusfb.c

+53 −66
Original line number Diff line number Diff line
@@ -327,9 +327,7 @@ static const struct { 
#endif /* CONFIG_ZORRO */



struct cirrusfb_regs {

	long multiplexing;

	long mclk;

	long divMCLK;

	int multiplexing;

};



#ifdef CIRRUSFB_DEBUG
@@ -461,45 +459,28 @@ static int cirrusfb_release(struct fb_info *info, int user) 
/****************************************************************************/

/**** BEGIN Hardware specific Routines **************************************/



/* Get a good MCLK value */

static long cirrusfb_get_mclk(long freq, int bpp, long *div)

/* Check if the MCLK is not a better clock source */

static int cirrusfb_check_mclk(struct cirrusfb_info *cinfo, long freq)

{

	long mclk;

	long mclk = vga_rseq(cinfo->regbase, CL_SEQR1F) & 0x3f;



	assert(div != NULL);



	/* Calculate MCLK, in case VCLK is high enough to require > 50MHz.

	 * Assume a 64-bit data path for now.  The formula is:

	 * ((B * PCLK * 2)/W) * 1.2

	 * B = bytes per pixel, PCLK = pixclock, W = data width in bytes */

	mclk = ((bpp / 8) * freq * 2) / 4;

	mclk = (mclk * 12) / 10;

	if (mclk < 50000)

		mclk = 50000;

	DPRINTK("Use MCLK of %ld kHz\n", mclk);



	/* Calculate value for SR1F.  Multiply by 2 so we can round up. */

	mclk = ((mclk * 16) / 14318);

	mclk = (mclk + 1) / 2;

	DPRINTK("Set SR1F[5:0] to 0x%lx\n", mclk);

	/* Read MCLK value */

	mclk = (14318 * mclk) >> 3;

	DPRINTK("Read MCLK of %ld kHz\n", mclk);



	/* Determine if we should use MCLK instead of VCLK, and if so, what we

	   * should divide it by to get VCLK */

	switch (freq) {

	case 24751 ... 25249:

		*div = 2;

		DPRINTK("Using VCLK = MCLK/2\n");

		break;

	case 49501 ... 50499:

		*div = 1;

	 * should divide it by to get VCLK

	 */



	if (abs(freq - mclk) < 250) {

		DPRINTK("Using VCLK = MCLK\n");

		break;

	default:

		*div = 0;

		break;

		return 1;

	} else if (abs(freq - (mclk / 2)) < 250) {

		DPRINTK("Using VCLK = MCLK/2\n");

		return 2;

	}



	return mclk;

	return 0;

}



static int cirrusfb_check_var(struct fb_var_screeninfo *var,
@@ -705,30 +686,27 @@ static int cirrusfb_decode_var(const struct fb_var_screeninfo *var, 
		break;

	}

#endif

	regs->mclk = cirrusfb_get_mclk(freq, var->bits_per_pixel,

					&regs->divMCLK);



	return 0;

}



static void cirrusfb_set_mclk(const struct cirrusfb_info *cinfo, int val,

static void cirrusfb_set_mclk_as_source(const struct cirrusfb_info *cinfo,

					int div)

{

	unsigned char old1f, old1e;

	assert(cinfo != NULL);

	old1f = vga_rseq(cinfo->regbase, CL_SEQR1F) & ~0x40;



	if (div == 2) {

		/* VCLK = MCLK/2 */

		unsigned char old = vga_rseq(cinfo->regbase, CL_SEQR1E);

		vga_wseq(cinfo->regbase, CL_SEQR1E, old | 0x1);

		vga_wseq(cinfo->regbase, CL_SEQR1F, 0x40 | (val & 0x3f));

	} else if (div == 1) {

		/* VCLK = MCLK */

		unsigned char old = vga_rseq(cinfo->regbase, CL_SEQR1E);

		vga_wseq(cinfo->regbase, CL_SEQR1E, old & ~0x1);

		vga_wseq(cinfo->regbase, CL_SEQR1F, 0x40 | (val & 0x3f));

	} else {

		vga_wseq(cinfo->regbase, CL_SEQR1F, val & 0x3f);

	if (div) {

		DPRINTK("Set %s as pixclock source.\n",

					(div == 2) ? "MCLK/2" : "MCLK");

		old1f |= 0x40;

		old1e = vga_rseq(cinfo->regbase, CL_SEQR1E) & ~0x1;

		if (div == 2)

			old1e |= 1;



		vga_wseq(cinfo->regbase, CL_SEQR1E, old1e);

	}

	vga_wseq(cinfo->regbase, CL_SEQR1F, old1f);

}



/*************************************************************************
@@ -904,6 +882,17 @@ static int cirrusfb_set_par_foo(struct fb_info *info) 
	/* formula: VClk = (OSC * N) / (D * (1+P)) */

	/* Example: VClk = (14.31818 * 91) / (23 * (1+1)) = 28.325 MHz */



	if (cinfo->btype == BT_ALPINE) {

		/* if freq is close to mclk or mclk/2 select mclk

		 * as clock source

		 */

		int divMCLK = cirrusfb_check_mclk(cinfo, freq);

		if (divMCLK)  {

			nom = 0;

			cirrusfb_set_mclk_as_source(cinfo, divMCLK);

		}

	}

	if (nom) {

		vga_wseq(regbase, CL_SEQRB, nom);

		tmp = den << 1;

		if (div != 0)
@@ -917,6 +906,7 @@ static int cirrusfb_set_par_foo(struct fb_info *info) 


		DPRINTK("CL_SEQR1B: %ld\n", (long) tmp);

		vga_wseq(regbase, CL_SEQR1B, tmp);

	}



	if (yres >= 1024)

		/* 1280x1024 */
@@ -1106,7 +1096,6 @@ static int cirrusfb_set_par_foo(struct fb_info *info) 


		case BT_ALPINE:

			DPRINTK(" (for GD543x)\n");

			cirrusfb_set_mclk(cinfo, regs.mclk, regs.divMCLK);

			/* We already set SRF and SR1F */

			break;
@@ -1179,7 +1168,6 @@ static int cirrusfb_set_par_foo(struct fb_info *info) 
		case BT_ALPINE:

			DPRINTK(" (for GD543x)\n");

			vga_wseq(regbase, CL_SEQR7, 0xa7);

			cirrusfb_set_mclk(cinfo, regs.mclk, regs.divMCLK);

			break;



		case BT_GD5480:
@@ -1257,7 +1245,6 @@ static int cirrusfb_set_par_foo(struct fb_info *info) 
		case BT_ALPINE:

			DPRINTK(" (for GD543x)\n");

			vga_wseq(regbase, CL_SEQR7, 0xa9);

			cirrusfb_set_mclk(cinfo, regs.mclk, regs.divMCLK);

			break;



		case BT_GD5480:

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